Noticed yesturday that there was a rattle coming from my engine bay. It starts right about 4200 rpm and promptly goes away at about 4500 rpm. It's not very noticeable when driving by much more with good open. Doesn't matter if car is in gear drivin or just revving its still there. It's even there as the car revs down either in gear or when with the clutch it. It sounds metallic in nature. not sure where in bay is comig from though since I havet had anyone to hit gas for me while i listen. Any ideas?

I'm hoping it's not mechanical and its just something hitting something with just the right vibration. Or maybe there is a weird spot in the stock tune that comes out because of my mods when it's revved up. It's possible it's been there and I've just never noticed but I was dragging yesturday so it was wound up quite a bit. Hoping I didn't do damage but it's hard to believe that I could and only have the noise for 250-500 rpm range.

 

Just for the heck of it, make sure the heat shield at the fire wall (below the PS pump reservoir) is not bent down and into the exhaust manifold cover....Seen that cause what you describe.

 

That was actually my first thought and wasn't the problem. Turns out it was the center bar on the alta air diverter. At that rpm it vibrates just right and buzzes against the intercooler. Was quickly found once I had a buddy rev the car for me so I could get under there and listen.

 

Glad you found it! It's fortunate that you were getting the buzzing even without the engine being under load - makes the troubleshooting MUCH easier!

 

Yes. Just out of curiosity. What kind of noises can you get under load?

 

Well, just as an example, you probably wouldn't have been able to duplicate engine pinging or knocking by revving the engine in neutral, since there's no real load on the engine. Same with engine bearing noise, unless the bearing was really badly worn. Once, a friend's MINI would make a knocking noise under the hood, but only when turning at slow speeds. It turned out to be a leaky engine mount. Noises are just so much easier to diagnose if you can listen to them from outside with the car not moving.