I have a 91 v8 automatic and had my transmission replaced about 3 weeks ago. Along with that, I had the serpentine belt replaced as well. I know it's supposed to give a little and it seems pretty tight. However, there were no issues when I first picked up the car. I started hearing this high-pitched buzzing sound coming from the alternator about a week ago and figured I'd get it checked out "later". Well, about 2 or 3 days ago it got REALLY loud and started smelling funny. I compare the sound to the buzzing a fly makes, you know like in movies. So would a tight belt result in the smell and noise or am I going to have to get my alternator replaced?

Anyway, it makes this sound even at 2000 rpms and just sounds worse the higher they go. I don't know if it makes a difference, but today when I started it the rpm needle was moving a little back and forth. It completely shut off the other day when the noise started getting loud and I was scared to drive the half mile I had to get home because of the smell.

I'm completely obsessed with this car and I feel bad when there's something wrong. Everytime I get something done to it I ask the mechanic if there's anything ELSE that will make it better and none of them have ever said anything about the alternator.

 

Buzzing sounds like a belt that's too loose. How far can you push the belt on the longest stretch with your index finger? The auto tensioner should keep it to... what, maybe 1/2"? If that's going bad it'll "flap" in the breeze and sound like a bumblebee.

If it's loose the belt will slip and it'll heat up the belt. Does it smell like burning rubber belt? Is the running surface of the belt slippery and greasy? (after it was running?)

 

The belt has a tensioner that's spring loaded; always puts the exact same amount of tension on the belt. It can't really be too tight or too loose, unless the tensioner is messed up.

Are you SURE the sound is coming from the alternator? Try taking a piece of heater hose, and stick it in your ear (!!!), and use it like a probe to isolate the EXACT source of the noise.

 

It barely gives a 1/4 in. But I would think that if THAT was the problem it would've been like that right out of the shop, not a week or two later. The belt isn't greasy. It's dry as a bone. And the smell... I don't know, it doesn't smell QUITE like burning rubber, I really think it's coming out of the alternator. Today when I was looking at at and pressed the gas the alternator jumped a little, it wasn't running totally smooth.

 

?!?
Ok, not too loose then.

Remove the belt and start the car. It'll set off all kinds of warning bells, but that'll at least let you know it's something in the accessories. With v-belts you could just remove the alt, but you have a serp so you have to take them all out of the equation.

I'm guessing your alt is just bad. Replace it and keep going.