I've used lead bitumen inside my 130, doors, floor pans, seat box etc. It's a relatively cheap way for sound proofing and easy to apply using a HD hairdryer. You'll need a combination of both anti drumming noise and sound deafening materials like foam structures. In my 109 I'ved used the noisekiller stuff, main problem is that it comes loose + not fit smooth to the panels. I've spend a lot of energy in getting the noise down, best improvement on the motorway is a higher ratio, so fitting an overdrive.
Cheers
Marco