240SX header 3" cat 80mm exhaust sounds like exhaust leak at 4.5k+?

[alkemyst]

I have a KA24DE with OBX header, random 3" cat, and the 5Zigen Pro Racer 80mm.

I am a little pissed the OBX came with a slotted flange for each bolt rather that a single hole on each side...my 3" cat is much bigger than the collector. I have backed the header flange to cat bolts with large washers.

At 4.5K+ or so it still sounds a bit more harsh than rumble...almost like an exhaust leak or V8 running dynomaxes.

Is this sort of normal sounding for a KA24DE?

I can't find an actual exhaust leak (no 'soot' on the flanges at all)...I'd really like to jack the car up and have someone rev the shit out of it, but at that point I may just drop it off at an exhaust shop and for $50-100 bux have them reweld two new flanges that are perfectly mated.