Loud intermittant whining/buzzing sound from under hood.

[Mbrooks420]

Occasionally when I am driving, usually very little throttle or just letting off the gas, I get a buzzing/whining sound that comes from somewhere around the engine. If I rev the engine a little over 2k the sound goes away. As the rpm's go up the sound gets softer. It sounds a lot like alternator whine you would get with a stereo. I have tried turning the lights, radio, heater,and ac on and off. Nothing changes it. Neither does shifting gears, or anything else I can find except revving the engine. Any ideas on what it could be? I suspect maybe the alternator, and maybe having to do with a low voltage problem, caused by low rpm. As far as I know it is the original and has 115k on it.
Any ideas on where to start, or what it could be??

 

[sapogmxr]

is it a really loud hum?

 

[Mbrooks420]

Yeah, It could be classified as a hum. It's quite loud. You can hear it with the windows up and the ac on full.

 

[sapogmxr]

If the noise is coming from around your intake tube it might be your IAC. This is a great thread on it. http://www.explorerforum.com/forums/showthread.php?s=&threadid=52885&highlight=loud+hum

 

[Mbrooks420]

I had a new IAC put on about 36k ago, so its prob. due for a cleaning.