hey guys i have this strange resonance/humming/ringing nose that is coming from my engine/exhaust at low rpms. its occurs at the same exhaust RPM everytime and is not the drivetrain as it still does it with the clutch disengaged. car is a stock ppw 2005 enthusiast 6spd. it is a pretty annoying sound. what gives?
any ideas?
thx

 

I've noticed the same thing on my '05. However, I only notice it when I first start the car cold and I get out and stand behind the car. It seems to come and go as the car is warming up. After the car warms up and the idle drops down under 1k rpm, the sound is gone until I start the engine cold again. I definitely can't hear it when sitting in the car, even with the windows down.

It does sound exactly like what you are describing though; a faint metallic humming/buzzing/resonance at idle from the (stock) exhaust. Not sure what to make of it.

 

Could be a result of the catalytic converters being burnt enough to start breaking down. If its a metallic sound, it could be a heat shield that has torn/cracked and started rattling, once the metal heats up it goes away...

Just my thoughts.