I think I may be such a dumbass that I destroyed my engine!? Help!
So I could give a really long back story but Ill try to keep this short, the tl;dr is that I’ve been driving with a bad MAF for way too long and now I have a loud knocking coming from the engine. I already did the timing work last year, and it ran fine when I got it back together. The MAF started going bad a few months later and I’ve been trying to diagnose it and other issues ever since then, just today found out that the MAF was the main thing all along but now I have the knocking which seems really bad.
So, I first noticed it a couple weeks ago. My main cats were apparently clogged so I gutted them and reinstalled the downpipes. I went for what was originally supposed to be a short test drive and found that this fixed several issues I had with throttle responsiveness and shifting, but my fuel trims were still going lean under load. I figured this was probably just an exhaust leak so not a big deal (2 reasons: I was rear ended a while back and still thought there might be a cracked manifold or something causing my issues, and because I think one of the downpipes isn’t fitted exactly right so it needs to be readjusted) and I ended up going on a longer and more “spirited” test drive than I probably should have. After about 30 minutes when the engine fully warmed up, it started to make a really loud terrifying knock. After it started knocking I shut it off and let it cool down for about a half hour and then started it up again, and it wasn’t knocking anymore. another 5 or 10 miles down the road and the knock came back. I got it home and parked it in the driveway overnight, the next day on a cold start I noticed a short rattle (I still occasionally hear this after doing the timing, but only the “normal” <1 second rattle) except this time the rattle sounded different, it sounded like it was the same knock I was hearing before. It didn’t knock after the engine fired up, though. I decided to drive it because “If it’s a bearing it’s already fucked anyways, and if it’s the exhaust it’s no big deal.” and the knock came back again even quicker than the first time. this was all a couple weeks ago. Last week I happened to finally have a chance to test my old MAF on my friends S4 and found out that it was actually the cause of the fuel trims going lean under load (I had tried the unplugging it while running test early on but that didn’t tell me anything) so today I installed the new maf and started it up, and the engine cranked a few times before firing up and I noticed that it made that clunk during each of those initial cranks, but while it was running it didn’t. So my fuel trims are fixed now but I think it’s all for nothing because I destroyed my engine bearings! 
I’m pretty sure that one of my downpipes still needs to be readjusted, because that bank is still more lean than the other (which was never the case until the last time I removed and reinstalled the downpipes), and I know exhaust leaks can cause some really crazy knocking sounds from what I’ve read online, but I don’t think it could cause it to knock while cranking so now I’m really worried about my engine. I’m about to go readjust that DP again but I just wanted to ask, does this sound like a rod knock? I’m not really sure what types of knocks there are or what bearings can go bad besides the rods (I know I’ve heard of mains but not sure if there are more?).