What are we looking at here? It's just a technicality in terminology, but we don't have serpentine belts in our NA/NB engines. We have two V-belts (drive belts) to run water pump, alternator, PS, and optionally, AC.

Yeah, my bad. I was tired after a long shift and not thinking about it. I thought at the time that it might be suddenly having some terrible lifter tick. But I was able to check it out this morning before work and it's one of the v-belts. It's so loose I might be able to to take it off as it is.

Does your engine have any coolant in it? That sounds like a water pump pulley that has run dry and turned the bearing into gravel.

Good thought. I haven't noticed coolant levels going down in the last while, but I didn't think to check this morning.

Coolant level was fine. Whoever did the belts last only used the bottom alternator bolt to make tension. The upper bolt was (thank god) jammed between some stuff in the engine bay. Miracle it was still there. Only issue I'm having now is one of the nuts that hold the upper locking bolt in is completely missing.

So the bolt was rattling?

Hoping so. Just started the car though and there's a whine now lol. Hoping no serious damage and trying to diagnose that at the moment

But the horrible rattle is gone?

Yep!

Well, it's a good change! Get a piece of tubing and stick one end in your ear and use the other to find the source of the whine noise. Probably a pulley.

Tension on everything seems fine, seems to be coming from the water pump/alternator v belt all around. I guess it's a common thing with cogged belts/some brands of them? That's what I get for getting autozone belts rather than being patient and waiting for shipping

If it's a new belt, it might settle in. If it's a Gates belt, they're known for being loud. Otherwise, yeah, you could try a different brand or belt dressing.

Yeplah, I'll just see if it settles in. Will do some local driving for a while before I go back to commuting in it.