Did you happen to change plugs when you did the pulley swap? I know after I did mine I had 1 range to cold and my car didn't like them so it would make that noise whenever the motor made boost. Plus you could feel it missfire, it ran amazing as long as there was no boost. I'm going to try and see if I can find a video that I took of mine when it was doing it........
Here is the link http://media.putfile.com/MVI_153468
I'm sorry it is so hard to hear but I was going like 70mph at the time.
1998 SSEi The Executive Hauler
Built Trans w/ 3.29s, P&P Jenny 5, S1X cam, Silver TOGs, Northstar TB & LQ4 MAF, FWI, Dyno tuned, #60 injectors,Oil Pressure Kit, 2.9-3.4MPS, MagnaFlow exhaust, 3" HF cat, MSD Coils & 8.5mm Super Conductors, AeroForce, only Sunoco 94, 100