Weird ringing noise?
 

Hey guys, quick question. Last night on my way home from work I was driving my 99 D2 with the drivers side window down, and I noticed when I accelerated into the 1-2 RPM range, I heard a slight (almost non-existent)
ringing noise. It's hard to explain how it sounded, it wasn't really a chirp or squeal sound, it was more like a quiet continuous ringing. I was unsure at first if I was hearing outside noises or if the truck was making the noise, I also thought it could just all be in my head. I've heard the noise before, but it doesn't seemed to have caused any problems. I'm not sure if this would be classified as a 'squeak' or 'chirp', but I know that a squeaking sound could be linked to the gears, water pump, power steering pump, etc. A chirping sound could be the front driveshaft, but it really didn't sound like either one. As i said, it was more of a ringing. Like a quiet high pitched hum, like when you get a 'ringing' in your ear. It could have just been regular engine noise, but I want to be sure. Have you guys heard this noise before? Any ideas what it might be? Is it a problem? Or should I not worry about it?

I see this thread is a bit older, however curious as if you'd ever discover the culprit.
I seem to have a faint "ring" from what sounds like passenger front.

Any noise is annoying but somehow if you think its coming from passenger front and inside, could be the a/c blower. Something got stuck. Could be one of the pulleys in engine. Lubricate them one by one, you might get lucky to find which one.