I read a thread on here the other day about someone who had a problem with a housing association resident. Mine's the other way round. The house next to us (50's terrace) used to be a council property, untill the occupiers purchased it. They were great, although the garden was left to grow long, we never heard a thing. Unfortunatly, they couldn't keep up the repayments on the house and lost it to the bank. The house was auctioned, and a young couple moved in. They immediatley went on a blitz of DIY, garden was landscaped, porch built and the like.
About this time my wife gave birth to my son. 2 days after she got out of hospital I had to go round at 11.30pm and ask him to stop drilling into the party wall. During the hot summer (son's window open due to the heat) I had to politley ask him if he could leave mowing his lawn to a more sociable time than 10pm. All tiny little things, that he always acknowldged with a "Oh, sorry mate, didn't realise the time". No dramas.
They then ripped all the carpets out of the house and laid laminate flooring, unfortunatley without any soundproofing underneath. They fitted UPVC doors themselves as well. The upshot is that I can hear absolutley everything. I know what they're having for tea. I know when they're having trouble with the bank. I know when they're having sex. I know, even, when they turn the light on and off. We worried how to broach the subject. Then the parties started.
They'd made friends with a few of the neighbours (I never had. Just a passing "hello" as their social lives revolve around pubs and drinking). They started all going round next door, as they had the larger living room. It was every Friday, and it drove us up the wall, but we kept quiet and didn't say anything as there's not a lot you can do. They had a lot of kids over, and the doors started slamming. The vibration from that is hard enough to make the picture frame on the night stand fall over. And being kids, they were running in and out of the house every minute or so.
Then the parties increased. 2 or 3 times a week. Running till 3 am or so at the weekend with impromptue karaoke by then end. I wouldn't mind if they could sing. 
I mentioned in passing a few times that we could hear them, but didn't complain.
Fast forward 6 months to last Christmas. Around the 18th the parties started. 5 nights on the trot. I got so angry, but kept myself in check. Eventually, after the 1,235,690 time they slammed the door I went round. It was about midnight. "Hi mate, I don't suppose you could ask the kids to stop slamming the doors, it's waking my nipper up?". Unfortunatley, it would seem he'd had a bit of booze. He squared up to me, saying I did nothing but complain. I said I'd spoken to him twice, over 6 months ago. He got aggressive, took a step towards me. I told him I'd speak to him tomorrow when he'd grown up and walked away. I'm ex forces and didn't want to get in a fight with him, for one he was drunk and it wouldn't be much fun if I wasn't, and secondly my job at the time was teaching and I needed my criminal record check to be clean.
We never spoke again. For about 3 months after there was deliberate door slamming. Fireworks at 2am with drunking giggling. Music turned up to amazing levels at 4 am. They trashed a couple of bushes in our front garden (well, I asume it was them). My car gathered a few new scratches. I ignored it all. Eventually everything returned to it's normal (although still excessive) level. Due to their relationship with others, we became the pariah of our end of the street, however those opposite and to the end sympathised with us. The attitude of all but our immediate neighbours softened though, and after a few arguments with next door (we could hear those quite clearly, obviously) the parties have stopped, and this Christmas we got cards off all of them except those next door. The parties are more like once a month now, although they still have his sister's kids round every Friday, with the associated slamming doors till about 11pm.
All of this has no relevance to my question. 
Sorry if you've read this far expecting advice on the above. I've learnt to live with all that and I just needed to get it off my chest.
My question is about the noise now. We can still hear footfall, talking, TV, sex, light switches etc... I've looked into soundproofing, but I'm unsure how to go. This would be a significant investment for us (we only redecorated last summer, so would need to be done again). Are there any sound engineers on here? Can you point me in the right direction? Cost isn't an issue to a point. I just want to stop the noise, as to move house will lose me my 2.5% mortgage as well as the circa 10k to move.
I hope someone can help, it's driving me up the wall. If it helps, party wall is single skin brick. We have a split staircase wall, bedroom wall and living room wall (which includes an open fire place, you should hear him throw logs in it!).
If you can't help, thanks for reading anyway. My poor wife is at her wits end. Even my 18 month son shouts "BANG!" everytime they slam the door now. Unfortunatley, I work overseas, so she has to deal with it herself.
