Squeaking after New Alternator Install

On Tuesday, I had a mobile mechanic come and swap out by bad alternator with a new one I got. Drove my truck to work and back that afternoon with zero problems or anything I could notice. Wednesday morning, I start my truck up to head to work and there's a horrific squeaking/screeching noise. I drove to work thinking it might just be moisture/cold in the new alternator pully, but it only quieted at lower RPMs and never fully went away. I texted the mechanic who said it was probably an overstretched belt and worn out tensioner, but I don't understand how that could be since the squeaking noise wasn't present before he swapped out the alternator. It sounds like it's coming from the alternator pulley, and I found that spraying a little WD-40 on the bearing makes the sound go away for about 10 minutes of driving. Then it slowly starts to creep back. I don't plan on adding any more WD-40 because I know it's not good for the rubber in the belt.

Has anybody else had a similar issue with a new alternator and has any recommendations? I've heard from lots of folks that even new, non-reman alternators like the one I got can have problems right out of the box. Was planning on driving a few hours away to pick up chairs this weekend at my parents house, but now I don't feel confident I can make it there and back without getting stranded.

UPDATE: I took my truck in to the mechanic and it was in fact a worn out timing belt. In addition, the mechanics pointed out that my lower control arms were shot and needed to be replaced, so I'm glad I ended up taking it in for them to look out.

 

Welcome to TW..you swapped the belt?

 

Loose belt.
Good luck with your truck.

 

Post us a pic. Welcome from Denver!

 

No I didn't swap it out - it's not brand new but still in decent shape. Got it changed out just over two years ago.

 

If the Alternator is still bolted in place....and you mentioned spraying WD on the pulley makes it stop?

 

Triple check the routing of the belt. It’s possible to get it on and have everything work, but not have it routed around the idlers the right way so the tension is too loose. The proper routing is a little unintuitive.

I’ve made that mistake. Changed my belt, installed the new one in a way that looked right and made sense in my head, and got an ungodly squeal, especially under any electrical load, until I looked up the diagram of how it’s *supposed* to look. The tensioner was noticeably much tighter after fixing it right.

If it’s routed right, and you’re 300% sure of it, could be a bad tensioner.

 

I did that too