Weird engine noise HELP!

Hello All I have a 91 Talon non Turbo. I just replaced all the belts and I mean ALL of them. Everything went well. However there is the strangest engine noise I have ever heard coming from the valve cover area/front of engine. To be totally honest it sound like a loose heat sheild vibrating.....it is a rather loud Brrrrrrrrrrrrrrrrrrr sound if that makes any sense. It comes and goes at certain RPMs....the engine itself is NOT vibrating, I have plenty of power and the engine is running smoothly, EVERYTHING seems fine except for this loud noise....its driving me nuts! I removed the valve cover because I thought maybe one of the cams was loose in the journals....no luck, everything is nice and tight under there as it should be....I cant find anything wrong. It is not a grinding sound.....not ticking.....I do NOT suspect crank walk.

* Things to note......I had this noise BEFORE the belt change
* I had a broken "silent shaft" belt (belt that goes to the left under the front cover.....goes from crank to the left....not balancer shaft belt.
* Everything is assembled properly
* The noise is still there with no accessories hooked up

Hope someone knows what this might be.....I have never heard anything like this in all my years working on cars.....well not true....I have heard a similar noise when a heat sheild vibrates....but that is it.

exhaust leak? check all the connections on the exhaust mani to head and exhaust mani to down pipe

Nope....no way. Thanks tho.

My car does this too. I had just rebuild my motor and when i rev it up tp around 4000 rpms it does the same noise as you describe it. dont know what that is but before they rebuild it, it did not do that. I have a 95 gsx. My friend gots a gst and it doesnt do that either. Im thinking of what gthompson said about the exhaust leak. What my question is that would the car loose power if you have an exhaust leak and would it be smoking through the exhaust because when they rebuild my car it was slower and with that noise and also alot of smoke through the exhaust. My car at low rpms im guessing it responds alright but at high rpms it does not run clean like it is forcing itselft from 4000/4500 to 7000 rpms. I hate it.

When was the last time the oil and filter was changed. A friend of mine was telling me about a similar problem(hesitation from about 4000-7000) He told me he changed the oil and filter and it cured the problem.

When was the last time the oil and filter was changed. A friend of mine was telling me about a similar problem(hesitation from about 4000-7000) He told me he changed the oil and filter and it cured the problem.

well i have changed all that. they told me that my timing might be off but since i dont know anything of that, dont know what it could be. What i do know is that my car before they rebuild it, it had alot of balls and now its slow way slower.

if it's just a small exhaust leak you won't have any loss in power or any smoking at all, it's just an annoying almost like a deep buzzing noise. i had one and it pissed the hell out of me. check your exhaust gaskets, i'm almost willing to bet that's your problem.