[HiFlow5 0]

You said it sounds like its coming from the passenger side of the engine bay, correct? Now isn't that the side the supercharger is on? I'm still pretty sure its an internal belt problem with the Powerdyne. Do a search on a some of the mustang message boards about the problem, see what you come up with. Or even give powerdyne a call, see what they say about belt slipping. I would replace the serp belt if its cracked, you don't want one of those snapping while your miles from home!