It looks like you have resonators in place now, you could cut those out and replace with a product that is known for quieter sound.

I do agree with what has been said, replacing this entire system with a stock exhaust will be a sure way to go back to factory dead-quiet exhaust. Check your local BMW junkyards, Craigslist, eBay, and forums. My guess is you could have the complete system for $250 or less.

What do you know about this exhaust system? Does it have a brand stamped on it? Or was it done custom? It's possible that it is stock all the way back to the mufflers in which case simply find a different muffler and weld it on.

__________________
2002 X5 4.6is - Titanium Silver / Black Alcantara - Dinan Stage 2 - Bilstein/Eibach - Brembo BBK ----SOLD---
1993 318i - Brilliantrot / Tan - bone stock daily driver