I had this same problem in my 2.4 sedan. Had the clutch disc and pressure plate replaced and i haven't heard the sound so far. I've only driven it 2000 miles since the replacement though.So for about the last 12,000 miles, I have been experiencing a loud humming noise from the front end of the car that only occurs when engaging the clutch from a dead stop with minimal throttle. The noise is comparable to a tuning fork that I can worsen by trying to start in 2nd or 3rd gear (3rd being worse than 2nd, 2nd being worse than 1st). If I try to start in third and I engage and hold the clutch in just the right spot, it will give me that very harmonic noise for the first couple of feet of movement. The noise is more intense when I am starting from a dead stop in grass or gravel (any surface with more friction) and MUCH worse (annoying) when trying to start up hill. I took it to the dealer (12,000 miles ago) and took the mechanic for a ride. He scratched his head and said he couldn't replicate the sound on the lift (since it only happened when there was a significant load on the wheels). His only theory as to what the noise was, was that there was a "harmonic vibration" coming from the catalytic converter that when there was just enough back pressure in the exhaust, it could cause the cat. to vibrate and create that tuning fork like sound.
Does anyone have any clues as to what this could be and what I could do to solve it?
I can take a video and post if anyone would like to see/hear it first hand.
I have a manual/2.4L koup