Hey everyone, i have a 1991 camaro RS V8... starts and runs fine, just did an air conditioning job... texas heat is too much. after i finished i noticed that the alternator starts "buzzing" when i turn the A/C on. alternator still works and the battery stays charged. a sign of it beginning to die? it just does it when a/c on. also there is a almost knocking noise that comes regularly just when the car is idling not when accelerating. doesnt seem to be hurting performance and goes away after accelerating. it seems to be coming from the rear of the engine on the left side. pretty noisy from the inside of the car. any ideas/ comments??

thanks.

 

Does the alternator sound like a buzzzzzzzzz or bzzzzzzzzzz? It makes a difference!
Sounds like it could be on the way out and the extra load is making it show it's age. Does it buzz like that when you have the headlights and other accessories on too (with the A/C off)?
The knock you hear could be an exhaust leak, the donut between the exhaust manifold and head pipe. Could also be an internal engine issue, such as a rod knock.
I don't spose you can put up any videos of your sound effects?

 

the extra load of the a/c can create some interesting noises at only certain rpms. your car uses 1 serp belt, right? if the tensioner is going bad, it can create a knock noise that will travel throughout the car, and can be amplified in the interior. or the motor could be going bad, but i try to be optimistic

 

Yeah I'm trying to be optimistic myself... hope its not the rod. The alternator is a bzzzz noise. Only when the a/c is on. Nothing else. The noise seems like its coming from the exhaust manifold but ill check today. I'll try and upload a video within the next few hours.. also if it was a rod knock wouldn't it be constant? It seems to go away after I accelerate.

 

yea, a rod knock would get louder with load. piston slap from a broken piston could go away once hot. an exhaust leak would get louder with noise. the buzz could be the bearings going bad in the alt and the extra load on the belt with the a/c on could be creating more pressure on them

 

It's not when it gets hot... its just when I accelerate that it goes away. Wouldn't a broken piston/slap make the cars performance be bad? I don't sense any drop in the cars performance... I'm not worried about the alternator really right now anymore since they are fairly easy to replace and they are cheap.