I'm on a tight budget but things i have done have made a big difference.
- Installed a radio and four speakers- fill the defender with vibrations you don't mind hearing!
- Ebay - Six pack of trimfix - and ten camping mats at £2.55 each free delivery from china - Fire retardant - foil backed - 6mm thick - closed cell.
Covered 100 % of the roof, under the headliner
Covered the entire rear tub with camping mats then covered with 3mm checker plate rubber for the floor.
Still have two mats left, but ran out of trim fix - will be doing the inside of the rear door ( which is a replacement as the other had an argument with a trailer and didn't seal - new door is much quieter )
Will also be doing behind the seats, over the seat box and i may well do all round the foot wells and bulk head and bits with it too - definitely reduces vibrations to something slightly more bearable.
The camping mats and trim fix are not expensive compared to other materials. £100 quid would give you enough of both to do the entire interior - I follow put foil tape over the joins and patches in awkward areas and things to finish up.
It does get a bit expensive when all that needs to be covered - the floor of the tub i have covered with rubber mat, new ss carpet retaining strip to finish it off - makes it look more finished but still just another cost.
because you have packed everything out by 6mm everything will be bigger so an off the shelf carpet kit like exmoor trim probably wont fit well. I still need to finish mine off so i'm just going to cover with that anthracite black carpet stuff.
added benefit of covering the floor of the tub with camping mats then rubber is that its not hard to kneel on when your scrabbling about in the back. Put black stixall round all the edges to seal the rubber. Stopped a lot of drumming.
My worst noises come from very rattly sliding windows, and the dash rattling which wanging a few self tappers through should sort.
