UK#1_Z28

I'm not to sure which board to ask this question because I'm not sure what the problem is. I'm new to posting on the board but I'm a long time reader. I have a 95 M6 LT1 with a few mods(headers,CAI,MAF,SLP Clutch,Exhaust) and it has 125,000MI on it. It's not driven very much and sits a lot in the driveway. I recently started driving it a little more and noticed a whistling/rubbing type noise coming from the backside of the engine?? Maybe, not really sure exactly where it is coming from. Also, this morning i took it for a little drive and it seems to be running fine to me but the speedometer is not reading right and when you rev it up in neutral the mph goes up as well this noise. Any help would be greatly appreciated.