Serp Belt Noise Driving me Nuts!

About a month ago, I started getting some serpentine belt noise (a wispy almost whistling sound, not a chirp or squeal). Not surprising as I'm guessing there was about 70k miles on it. (Verified by squirting some belt dressing on it between the crank and ac pulleys and the noise disappeared.) All the pulleys were aligned properly. Belt was starting to show splits/cracks.


I replaced the belt, tensioner pulley and the idler pulley (tensioner shock was loose and vibrating). Started her up... still had the noise. In the past I've found new serp belts have to wear in a little bit, so I decided to wait it out.

700 miles later, I'm still getting belt noise... more noticeable than before belt replacement. I tried cleaning off the grooved pulleys with a stiff bristle brush, no dice. Alignment of pulleys is still fine.

Yep, I could just squirt a bunch of belt dressing in there, but that's like putting protmatter in your Genesis Device... short term gain, long term loss.

Have I missed something? Is there some other trick to try?

Check the alternator pulley for proper operation. It's a clutched pulley so if you block the alternator fan from spinning, the pulley should only spin in one direction.

Alternatively if you have someone who can watch the fan, if you spin the pulley the fan should only spin when you spin the pulley in one direction.

I'm currently doing the same tensioner+idler+alt pulley overhaul on mine and this is just what I've read. If the alt pulley is bad it introduces a lot of vibration and wear onto the rest of the pulleys, the belt, and tensioner. If you search around a bit it's a common failure point and if it's bad you'll keep going through tensioners and belts.

Alt pulley appears to be behaving properly. Spins free in both directions until you hold the fan, then only in one.

I had a similar thing recently although mine was more of a rattle noise. I changed all those belt parts and the alternator pulley and the noise was still there. Then my alternator died less than a week later and the noise stopped. A new remanufactured alternator went in and it has continued to be noise free.

In my case the noise was the death warning for the alternator. I don't know what is causing your noise but there are only so many things in the path of the belt.

Try squirting a little wd40 directly to the back of the alt pulley. Don't get any on the belt, and see if the sound changes or goes away. I'm betting it will.

While the engine is off and then start it up.

Tdijarhead said:

Try squirting a little wd40 directly to the back of the alt pulley. Don't get any on the belt, and see if the sound changes or goes away. I'm betting it will.

While the engine is off and then start it up.

Click to expand...

No change.

I guess the next step is to pull the belt and degrease/clean all of the pulleys...


On that alternator note, I did notice the following: When I start the car my scan gauge registers the batt voltage then the alternator output after the engine catches. Normally, the change is instant. I noticed yesterday and today that the voltage drops to 7 or 8 volts once the engine starts, then over the next 30 seconds or so the voltage comes up to a steady 13.9...

does that mean I'm looking at a failing alternator?

Does engaging the ac comp change the sound.

I think your alternator pulley is fine from that little test. If it had been bad the wd 40 should have quieted it right down.

Yeah my scan gauge is pretty much instant to 14v so yeah it looks like your alternator is on the way out. On a good note at least it's trying to warn you. Save the pulley there is a special tool to take them off. Often it's just the pulley that fails and a new pulley is about $60.

elroy said:

Does engaging the ac comp change the sound.

Click to expand...

Not in the least... (good idea though... I hadn't tried that).

Bengoshi2000 said:

On that alternator note, I did notice the following: When I start the car my scan gauge registers the batt voltage then the alternator output after the engine catches. Normally, the change is instant. I noticed yesterday and today that the voltage drops to 7 or 8 volts once the engine starts, then over the next 30 seconds or so the voltage comes up to a steady 13.9...

Click to expand...

ECU will not work under 9.6 volts. (iIrc)
I would check with a voltmeter and an assistant.
Maybe check the voltage from the negative post of the battery to the case of the alternator when the assistant starts the car.
I would not want to see more then a few tenths of a volt.
A meter with high/low capture would be nice.

Spent a couple days compiling numbers.

Battery reads 11.9

Once started, voltage drops to 10.9-11.1. Over the next 30 seconds it comes up to 13.8 (and hovers around that mark... it never exceeds 13.9).

My initial statement about 7 or 8 volts was incorrect.

Might run the motor with that belt off, just to sure it's not something else.

Bengoshi2000 said:

Spent a couple days compiling numbers.

Battery reads 11.9

Once started, voltage drops to 10.9-11.1. Over the next 30 seconds it comes up to 13.8 (and hovers around that mark... it never exceeds 13.9).

My initial statement about 7 or 8 volts was incorrect.

Click to expand...

11.9 volts is low for a battery, 12.6 is full charge. (car not running)
Taking 30 seconds for the voltage to come up does not sound right.
Try charging the battery and taking it to one of the auto parts stores that can give you a free test.
Keep in mind bad grounds can raise havoc in electrical systems.

Just posting back that the solution was replacing my alternator. I found a brand new Bosch at Amazon for $170. The whishpy noise is gone and I'm getting solid numbers out of the alt.

Thumbs up!

Reading through the thread, looking at the alternator was going to be my suggestion.
I had similar symptoms, kept trying different things, until it got really bad...then one day, the car wouldn't start...couldn't even turn the engine (push-start attempt wouldn't even budge it). Alternator had completely locked up, and the serp belt was holding the engine.