I have a 3 bed semi (built early 1960's) with the living room/main bedroom adjacent to next doors. The wall is two solid bricks thickness & very dense/hard bricks. Internal walls are also solid. Despite this, noise is a problem & the solid walls seem to actively carry noise through them. Upstairs I put up a stud wall, 2 layers of Wickes insulation board, & two layers of plasterboard (skimmed). Also isolated the frame from the wall/floor with some carpet felt. This had a massive effect on noise transmission. Downstairs, I think a lot of the noise comes through the party wall underneath the suspended wooden floor. Unfortunately, the joists in the house run from side to side (not front to back) & I think this arrangement transmits a lot of noise. When I redecorate the living room, I plan to put up another stud wall from the concrete sub-base under the floor up. I think a lot depends on just how considerate your neighbours are, whether they have theTV too loud or pushed against a wall, & worst of all, putting hi-fi speakers directly on the wall with no soft packing to limit the transmission. My girlfriends house is late 1980's build & the part wall is light blocks (can see in loft). Not sure if cavity (suspect not) but can hear just about everything from next door through this. Next house will definately be detached.