Sounds more like rubbing than knocking. Have you checked the belts? If your battery is dying maybe it's alternator?

 

Thanks for the quick response! I have not, I thought about that yesterday but kind of just skimmed over it as I had it in my head that it was a knock. Although that makes sense and I see what you're saying, I looked at the belts that I can see at a quick glance and they look ok. I am going to check the alternator and belts in a few minutes. Fingers crossed! I will post back what I find.

 

Doesn't sound at all like rod knock. Drive belt is a good idea. Mine recently had loosened to the point of squealing like crazy on cold starts. Makes sense why you're battery randomly died too.

Get a Gates Krikit Gauge. Stupid easy to use to check belt tension. Only need your hand. Nothing needs to be removed. Should be 110-144 lbf during inspection.

 

@a5m thanks! This is very helpful information. I am going to take a look later today. The car is under warranty so if I end up needing to I can just take it in, but if it is something simple I would rather fix it myself and not have to have my car towed and have the car in the shop.

 

Update: checked belts, took measurements with a friends gauge and readings were good. Including a video picturing the belts.

Dropbox

www.dropbox.com

 

Also, started the car again for a friend to hear and recorded it. We shut the car down quickly as he advised. Video has been uploaded and might give better quality.

Dropbox

www.dropbox.com

 

Doesn't look like it's the belts. Sounds different in the engine bay. Still not quite like rod knock, but I'm definitely not an expert.
My next step would be to check the belt tensioner, beyond that I'm not sure what else would be making that sound.
You could try to spin it by hand and see if you notice any sound.

 

Update: brought the car into Subaru and they got back to me letting me know it is not a simple fix and will need to take the motor apart to figure out exactly what the problem is.

I am now wondering what could have caused this to happen and if it is common. The car has just about 20k miles it was purchased about a year and a half ago, fully serviced, never missed an oil change or any preventative maintenance.

 

As usual, a newbie wants advice and there's not enough information to be of real help. So many questions...
Then we get to the last video and it definitely sounds like rod knock/piston banging into head.
I'm puzzled about the battery dying on you. Might be coincidental or perhaps you've had signs of the battery going bad.

 

Sounds similar to mine. I have a stock ‘19 sti and it’s currently at the dealership for an engine rebuild. I have 28k miles on mine. The more I read up on this issue (blown motors/rod knock) with the newer sti’s the more common it’s becoming. As far as the power loss, could be the battery getting drained while the car is off. Currently there is a lawsuit against Subaru for this issue for a couple different years, makes and models.
battery lawsuit link -https://topclassactions.com/lawsuit-settlements/lawsuit-news/subaru-battery-drain-class-action-settlement/
Really unfortunate man. I wanted this car for 15 years and waited and saved up. Finally got it and the engine blows. I take very good care of my car and don’t drive the balls off of it. Some people say I just got a lemon or the previous owner did damage and dumped it before it blew. I want to believe that but as I read in to it, it’s more common than you’d think. I’m still waiting to hear from dealer to find out exactly what happened. But a new car with that low of miles shouldn’t be blowing up so soon. I personally think there’s something wrong with them from the factory and it’s only a matter of time til there’s another lawsuit brought against Subaru. Yours is newer than mine so I would assume it’s still under warranty? Mines getting fixed at no cost to me but they’re putting the exact same motor in it (ra short block) new and reusing what they can. I think I’ve decided to sell mine as quick as I can because if it is a factory defect, who’s to say this isn’t going to happen again in another 20-30k miles when it’s out of warranty. If I had unlimited money to dump into this thing it would be a different story, but I don’t and don’t want to risk this happening again.
Best of luck getting it all sorted out.

 

It def sounds like rod knock. I had a 16 with 28k miles and mine sounded like that but way quieter. You have a warranty im confused why youre trying to figure it out yourself when a 2 year old car is covered under warranty.

Now the shortblock issues from my understanding goes to 2018. The 2019 models are supposed to be free of the rod bearing issue that has plagued most sti owners. I kinda want to say the new stis use the type ra block but i could be wrong.
Regardless that sound isnt an easy fix, i cant imagine the dealership not having to look inside the block.

ps : there were 5 stis at the dealership with blown engines when i took my car to subaru last week lol.