Name That Sound

I've got a 95 with 153K miles on it that is making a strange sound. Here are all of the specifics:

1) Sound is engine related
2) Sound is noticable from about 1600 to 2100 RPMs
3) Sound is definitely not present at idle
4) Sound is definitely related to engine RPM, it is present in any gear, as well as in park.
5) I'd describe it as a moaning kind of sound, not grinding, not whistling, not squealing, not humming.
6) From inside the car, the sound is coming from the passenger side.
7) From under the hood the sound is coming from the passenger side, kind of towards the front of the vehicle.

I've just finished some R&R on some front of the engine components, namely the tensioner and idler pulleys, as well as the power steering pump and the serpentine belt. So these components can be ruled out.

Any of you guys who have had the grenaded AC pump or had an alternator go bad ever experience this kind of noise? I've just never dealt with a noise that was so predictably tied to the engine RPM like that.

When my AC compressor went it screamed.
If yours was at the rear of the engine compartment I would have said inlet manifold.
a moaning kind of sound can be air related. (air filter box?)
Ho Hum thats all.

Could It Be Your Power Stearing? When I Replaced My Ac Compresor And Got A New Serpentine Belt. Mine Moans From Time To Time Espicaily When Its Cold Outside

Is it only moaning when you're actually moving? If so, I would guess a bad wheel bearing, or possibly just a tune resonating through the frame. - both evident at certain rpm's / speeds.

It makes that sound moving or sitting in park, as long as the RPMs are between 1600 and 2100. I don't notice any changes with temperature, although I have only had it for a month and the weather is still pretty cold where I live.

I've replaced the front bearings, different noise that led me to those, as well as the power steering pump (different noise as well). Given the general area of the engine where it can be heard the best, it is hopefully external. The only internal thing that I could think of in that area would be the timing chain tensioner for the front cylinder bank. I'm leaning towards the AC compressor or the alternator, although I have never heard one sound like this or make noise on such a predictable RPM range. I just wanted to see if anyone had run into a similar problem.

When did you last have a new air filter installed?
Is your air filter box clamped down?
I know I'm goin on about the 'air' but it would be nice to have a cheep fix. Ehh

:smile:

I just replaced the filter a couple of weeks ago and the air box is still fastened securely. The sound is also coming from the passenger side front, so I don't think that it would be the air box.

If you can hear it at 2100, take a 1/4 inch heater hose and place on suspect part at idle and use the other end to listen. Chances are you will hear the moan up close. I've found many screaming parts this way. You might even try placing one end on the block to see if it's coming from inside. (redneck stethoscope works wonders)

Well, it occurred to me last evening that I could do a simple test to make sure that the noise was related to a component driven by the belt. I just removed the belt, started it up and revved it a few times. The result was no noise, so internal engine stuff is ruled out. Since I replaced the power steering pump and tensioner and idler pulleys, that kind of leaves the alternator and the AC compressor (sure hope it is the alternator...). So, this weekend I am going to pull the alternator and take it to be tested. I am hoping that the testing speed is enough to cause it to make the noise.

Problem solved. It turned out to be the alternator after all. I removed it and took it to be tested. Heard a little bit of a sound so I took a gamble and replaced it. Now the sound is gone.

The one thing I don't see in the replies is the harmonic balancer. It's right on the end of the crank shaft on the belt side. I had one shift on a 3800 Transport van last year with about the same mileage.