Strange Noise during slow/normal acceleration
 

Hi guys, I'm experiencing a strange noise coming from my car.

'06 RX8
6 Speed, 58,000 miles

This popped up right after I put in a new clutch.

Anyway, when the car is idling it sounds fine, but when I begin to accelerate slowly a sort of loud (almost like a rumble) becomes noticeable and then somewhere in the low to mid RPM range this noise sort of pops in and out rapidly.

If I accelerate hard the noise completely all throughout first gear and most of second till the higher RPMs when acceleration and power start to naturally die off.

Any ideas? I'll try to post a video or sound clip soon.