Shrill sound

I have a 96 Eddie Bauer with the 4.0 V6. I was driving home today and was going up a hill when I let off the gas just a little and a very shrill sound came from the front of the car. It seemed to go away some as a accelerated again. I stopped at a gas station and reved the engine up in park and neutral and could not duplicate the sound. When I got back on the road it returned somewhat more so when I let off the gas pedal going 35-45 MPH. Any ideas of what this could be?

Have you ever cleaned or replaced the IAC valve (idle air control valve)?
When it starts to go bad it will make a howling sound at idle and the engine won't idle very good.

Thanks for the reply. I have not checked that, and I will do so tomorrow night. After driving it more today, it seems it happens the loudest at 2100 or 2200 rpm's and mostly while accelarating. It does have a sort of rough idle sometimes. But it does sound like it can be air passing through something. Can I clean it well enough, or do I just need to replace it?

I tried cleaning mine a few times before I just decided to replace it. If I recall correctly it was $50-$60 at Autozone. It was also a piece of cake to replace.

I tried cleaning mine a few times before I just decided to replace it. If I recall correctly it was $50-$60 at Autozone. It was also a piece of cake to replace.

Rockauto.com is alot cheaper than autozone. Give it a try.

The sound could be just a vacuum leak, this will give you a ruff idle, and if the leak is small it will sound"shrill". Check your vacuum lines for wear or holes worn in them.

Thanks for all the advise. The sound has vanished. I was going to change the IAC out this weekend and look for leaky hoses but it might be hard to get motivated without the problem. I will most likely still check for any leaks, but I am going to hold off on the IAC unless the problem comes back. Again thanks for the help.

There is a service announcement on the dust covers on the front wheel bearings. The only time the noise is present is from 10-45mph when it is less than 50 degrees outside. Mine had the same symptoms and that turned out to be that.