I soundproofed my series 3 i had with carpet rubber crumb underlay(Duralay is its trade name) that i covered with latex glue to stop it perishing. Normally 40 quid a roll.
Worked a treat apart from Allied carpets came round and wanted to quote me for a nice brown shag-pile.
Ear plugs
They are Cheep Effective and you don't have to f*** around sticking stuff to you landy.
If you think your TDI 90 is noisy try a Series its the only way I have found to stop the missus talking.