once again, when asking for help to trouble shoot a problem, some info would be nice, why it cant be said to have basic info such as YEAR, MODEL, TRIM in a sig I dont know. and no your not the first person to ask without giving info, just letting you know that it can help.

My first guess would have been heat shield too, but just in case......

can you get it to make the noise when stopped and in neutral holding it at 2500rpm. the more info you can give the better, even if you think it may not be directly related to the prob.

you mentioned the supercharger, so I guess that narrows it down to first Gen. what about miles, what about other service that has or has not been done, ie: timing belt kit ? has that been changed yet ? could the belt be lose, could a tensioner be going?