Noise under hood

I realize it's difficult to point out an engine noise by explaination, but here it goes...

I had posted this before but didn't have much response. I have an engine noise (or at least coming from the engine area). It ONLY occurs between 1700-1750rpm and somewhere around 2800-2850 (not sure though)...it's basically a mix between a buzz and a rattle, that's how it sounds from inside the car. It's kinda like a drinking straw in a fan... It is load dependent, so it won't do it at idle. It will do it with the torque converter locked or unlocked, and when the TCC is locked, if you give more throttle and stay in that rev range, it gets louder (adding load). It will NOT do it in neutral at all. The only other way to duplicate it other than driving is to put it in drive or reverse, hold the brake and load up the engine to that rev range. I checked at an exhaust shop and they couldn't find the source. I checked with my regular mechanic and he suggested either supercharger or balance shaft...I pulled the belt off the SC and it was still there so that's not to blame.

How likely is the balance shaft or gears to make this noise? I'm going to pull off the accessory belt when I get a chance and see if it's an accessory/pulley making it, and I'm going to try with a stethoscope. I just would like any insight if anyone has had anything like this.

My mechanic says for sure it's coming from under the hood, he just doesn't know where.

is there any possible way you could post a sound clip or video?

So while trying to get a video of it tonight I noticed it does do that buzzing sound at idle, it's just a lot harder to hear, and to make it do it. I had a video of the interior and the engine bay but when I recorded the one from the engine bay, you can't hear the noise. Either the mechanic heard something else or you can't hear it in the engine bay at all, or it's being drowned out by the valvetrain noise.

Here's the interior video. The sound is faint through most of it, you can hear it best at 0:23 though...it's doing it the whole time...ignore the drone of the engine and you will hear it.

I wondered if it's an engine noise if it could be an idler pulley. I'm just trying to figure out what is engine load related and will only show up at specific RPM's...it's been on my mind for a long time now.

http://www.mediafire.com/?ynqwnmg55my

I'm not a mechanic but I have a 3800 na GT and mine sounded like that and it was the idler pully. It was hard to find too because the bearings didn't feel rough when I took the belt off. I finally just replaced it because it was driving me nuts and that fixed it. Of course with the SC I'm not sure if that would make anything different. I don't see how.
Rob

Mine was making a similar weird noise once and it was the bearings in the water pump. Have also heard bearings in the alternator make a noise also. Sometimes you just have to wait till it gets bad enough and hope it doesn't break out on the road.

So I finally found it, and of course it was something utterly retarded.

I got my buddy to rev it up while I checked under the hood with a stethoscope. I checked all pullies and couldn't find it. I couldn't even hear the noise well over the engine...

Finally I looked in the back and noticed the rear engine lift bracket vibrates a lot at that RPM, and there was a line touching it (not sure which one, it runs along the top of the firewall) so I moved the line back into place against the firewall and the sound is now GONE. Amazing how that tiny sound resonated so loud into the interior.

I feel a ton better now!

Nice, free fixes are always the best kind. :iceslolan

Glad you found it and it was nothing major.