Between a Magnaflow and now being lowered on the usual Koni/Epic combo, I get a squeaking from at least one heat shield in the rear. I trimmed one before with tin snips where it was rubbing through but now more have appeared. It only does it at a fairly low RPM and low speed from what I can tell but it is annoying. Can I just throw some self tappers into them and be done? Or will I risk damaging something important?