i recently bought a 2000 s2000 w/ 30k miles with a clean title. i bought it 3 weeks ago, and the engines sounds funny. for example, when i am cruising around 50mph and let go of the gas, the car starts to vibrate and sound till i press in the clutch or gas the car more.

 

is the rpms around 4000rpm when you do this? you may simply be hearing the clutch buzz upon deceleration. this is a known issue via TSB 054