Diagnosing grinding noise (only at high rpm)

m3_arch · 05-25-2008, 12:42 PM

Alright, so I've been reading through a bit of old posts and still not quite sure what the problem is with my sti.

Keeping in mind, my car was hit a little of a month ago, the opposing driver t-boned me going about 30mph.

The first time I heard it was yesterday when I was traveling about 45mph and came to a quick stop. While slowing I rev matched and downshifted to 2nd from 3rd. This is when I heard a high pitched rub/grind from what sounded like the center/back seat area of the car. At first I thought it was the rear passenger wheel since the wheel was actually hit in the accident and a few suspension parts were replaced. But after hearing it again I ruled out the wheel.

The sound is something like if you were to take a piece of paper to a fan blade, but more metallic sounding.

It would only occur in a short burst. Not a long continuous grind.

I went to try to replicate the sound to try to investigate as to where it was coming from and it doesn't always occur. Maybe 3/5 times. I managed to get the sound to happen again not while just downshifting, which began to rule out the idea of possible synchro wear, but taking the car up to 5k+ rpm and then releasing off the accelerator. The grinding could then be heard in short bursts as the car slowed down. I managed to hear it shortly while in 3rd as well, which makes me think it can make the sound in any gear, 2nd gear is the only gear where I can reasonably get up to that speed to have it occur without speeding.

Would changing the center and rear diff oil be of any help? the car has about 18k on it and has yet to be changed. From reading some people are saying every 15kish to be on the safe side.

I'm also considering just taking it to the dealership, but I'd like to get an better understanding of what possibly could be wrong before I do so.

Any opinions or suggestions would be great help

thanks

GT4604 · 05-26-2008, 08:35 AM

I just had a noise very similar to that (if I'm reading correctly) and with about the same frequency for about a day - after 2 weeks of a slight clunking sound from the drivetrain that was barely noticeable.

I hit a bad hole in the road and the slight clunk started, as well as a pull to the left every time I hit the gas. I'm actually still not certain the pulling to the left isn't an unrelated issue yet but it would make sense.

The high pitch grind started and then a day later then my car stopped moving and that whining sound was extremely loud every time I tried to move in gear. I could be in first gear with clutch out and be revving past 4 grand and moving barely 1 mph. I jacked it up this last weekend and it turned out to be my CV joint - specifically the cage portion of it that holds the ball bearings on. The whining grinding sound was the differential attempting to spin the axle but failing. My guess is that it was beginning to slip a tiny bit because it was damaged but still functioning when it was making the noise earlier in the day, because it was the same noise when it really broke later just about 100,000 times louder.

I kind of doubt you have this specific problem but it just happened to me.

Does your noise change in pitch to engine RPM/wheel speed?

If you want to check your axles put it on stands in the rear and take off both wheels. First attempt to spin the hub and each side and try to notice a difference. Mine was completely broken and able to spin freely on one side. PB blast or oil the axle nut which is in the center of the hub, and the linkage bolt and nut which is horizontal to the ground behind and below the rotor (it's a large bolt, 19mm I believe, and like 8 inches long). Take off the axle nut and linkage bolt and 'swing' the rotor away and pull the axle from the back until it's free. Pull it out of the differential, try your best to pull it as straight as possible to prevent damage to the seal on the diff. It's in there with a snap ring kind of thing so it just takes pulling it and it will pop off.

Torque specs on the bolts are 145 lb on the linkage nut 140 lb on the axle nut.

Edit: I forgot to say, the cage was in about 25 shattered pieces

rcplez90 · 05-28-2008, 06:12 AM

Does it only happen under high rpm (maximum) engine braking?

Or can you ever make it happen by just applying the brakes?

Are all of your CV joint boots intact? They can produce a gear whine..

Friend of mine had an old eclipse and a similar sound came from high rpm engine braking in 2nd gear and the problem was his synchros. But that was only 2nd gear (just food for thought)

m3_arch · 05-28-2008, 06:46 AM

Quote:

Originally Posted by rcplez90

Does it only happen under high rpm (maximum) engine braking?

Or can you ever make it happen by just applying the brakes?

Are all of your CV joint boots intact? They can produce a gear whine..

Friend of mine had an old eclipse and a similar sound came from high rpm engine braking in 2nd gear and the problem was his synchros. But that was only 2nd gear (just food for thought)

Only happens under high rpm engine breaking. I havent been able to check anything yet on the car, its been raining for the past 3 days and still plans to rain more. The sound isn't coming from anywhere near the tranny, so I don't really think its the synchro's since I can replicate the noise in 1-3rd, and I'm sure it'd happen in any other gear, but I haven't gone that fast to check it.

rcplez90 · 05-29-2008, 03:57 AM

Hmmm... Might it be something with the change in exhaust pressure? (I think it turns more into a vacuum at high rpm with no load, but dont quote me on that..) Anything loose in your exhaust system? SPt license plate holder buzzing up a storm?

05-25-2008, 12:42 PM	#1
m3_arch Junior STI Driver Car: WRB 06' STi Location: Omaha, NE Posts: 98 Join Date: Jan 2007 Trader Rating: (0)	Diagnosing grinding noise (only at high rpm) Alright, so I've been reading through a bit of old posts and still not quite sure what the problem is with my sti. Keeping in mind, my car was hit a little of a month ago, the opposing driver t-boned me going about 30mph. The first time I heard it was yesterday when I was traveling about 45mph and came to a quick stop. While slowing I rev matched and downshifted to 2nd from 3rd. This is when I heard a high pitched rub/grind from what sounded like the center/back seat area of the car. At first I thought it was the rear passenger wheel since the wheel was actually hit in the accident and a few suspension parts were replaced. But after hearing it again I ruled out the wheel. The sound is something like if you were to take a piece of paper to a fan blade, but more metallic sounding. It would only occur in a short burst. Not a long continuous grind. I went to try to replicate the sound to try to investigate as to where it was coming from and it doesn't always occur. Maybe 3/5 times. I managed to get the sound to happen again not while just downshifting, which began to rule out the idea of possible synchro wear, but taking the car up to 5k+ rpm and then releasing off the accelerator. The grinding could then be heard in short bursts as the car slowed down. I managed to hear it shortly while in 3rd as well, which makes me think it can make the sound in any gear, 2nd gear is the only gear where I can reasonably get up to that speed to have it occur without speeding. Would changing the center and rear diff oil be of any help? the car has about 18k on it and has yet to be changed. From reading some people are saying every 15kish to be on the safe side. I'm also considering just taking it to the dealership, but I'd like to get an better understanding of what possibly could be wrong before I do so. Any opinions or suggestions would be great help thanks This ad is not endorsed by this member. Please register or login to hide this ad.

05-26-2008, 08:35 AM	#2
GT4604 Junior STI Driver Posts: 123 Join Date: Jan 2007 Trader Rating: (0)	Re: Diagnosing grinding noise (only at high rpm) I just had a noise very similar to that (if I'm reading correctly) and with about the same frequency for about a day - after 2 weeks of a slight clunking sound from the drivetrain that was barely noticeable. I hit a bad hole in the road and the slight clunk started, as well as a pull to the left every time I hit the gas. I'm actually still not certain the pulling to the left isn't an unrelated issue yet but it would make sense. The high pitch grind started and then a day later then my car stopped moving and that whining sound was extremely loud every time I tried to move in gear. I could be in first gear with clutch out and be revving past 4 grand and moving barely 1 mph. I jacked it up this last weekend and it turned out to be my CV joint - specifically the cage portion of it that holds the ball bearings on. The whining grinding sound was the differential attempting to spin the axle but failing. My guess is that it was beginning to slip a tiny bit because it was damaged but still functioning when it was making the noise earlier in the day, because it was the same noise when it really broke later just about 100,000 times louder. I kind of doubt you have this specific problem but it just happened to me. Does your noise change in pitch to engine RPM/wheel speed? If you want to check your axles put it on stands in the rear and take off both wheels. First attempt to spin the hub and each side and try to notice a difference. Mine was completely broken and able to spin freely on one side. PB blast or oil the axle nut which is in the center of the hub, and the linkage bolt and nut which is horizontal to the ground behind and below the rotor (it's a large bolt, 19mm I believe, and like 8 inches long). Take off the axle nut and linkage bolt and 'swing' the rotor away and pull the axle from the back until it's free. Pull it out of the differential, try your best to pull it as straight as possible to prevent damage to the seal on the diff. It's in there with a snap ring kind of thing so it just takes pulling it and it will pop off. Torque specs on the bolts are 145 lb on the linkage nut 140 lb on the axle nut. Edit: I forgot to say, the cage was in about 25 shattered pieces Last edited by GT4604 : 05-26-2008 at 08:45 AM.

05-28-2008, 06:12 AM	#3
rcplez90 Amateur STI Driver Car: Silver 05 WRX STi Fav Mod: Coming Soon Location: West Long Branch, NJ Posts: 10 Join Date: Dec 2007 Trader Rating: (0)	Re: Diagnosing grinding noise (only at high rpm) Does it only happen under high rpm (maximum) engine braking? Or can you ever make it happen by just applying the brakes? Are all of your CV joint boots intact? They can produce a gear whine.. Friend of mine had an old eclipse and a similar sound came from high rpm engine braking in 2nd gear and the problem was his synchros. But that was only 2nd gear (just food for thought)

05-29-2008, 03:57 AM	#5
rcplez90 Amateur STI Driver Car: Silver 05 WRX STi Fav Mod: Coming Soon Location: West Long Branch, NJ Posts: 10 Join Date: Dec 2007 Trader Rating: (0)	Re: Diagnosing grinding noise (only at high rpm) Hmmm... Might it be something with the change in exhaust pressure? (I think it turns more into a vacuum at high rpm with no load, but dont quote me on that..) Anything loose in your exhaust system? SPt license plate holder buzzing up a storm? This ad is not endorsed by this member. Please register or login to hide this ad.