This problem actually occurred a long time ago and I am just now getting around to fixing it. But basically when I was driving I noticed that there was a code on the dash, P0442, small evap leak. I thought it was the gas cap, but I tightened it and its been on ever since. There is a also a strange mechanical sounding grind when i let off the gas, but never when I rev it up in neutral or accelerating at all. Even if I deceleration with the clutch in the sound isn't there. Any ideas what I should be checking out first. The sound came at the same time as the code and I read that evap leaks can cause noise like this.