Ah! Your MIL's neighbour and I could start a support group for survivors of musical noisy neighbours, Vivienne.
Neighbour boy is late teens and I get on well with him. He has a lot of shit to deal with, and music is the only positive thing in his life, really. I'd feel pretty bad complaining about it, tbh.
He plays electric guitar (not very well) which is a bit annoying, and keyboard synthey sort of thing, which I hardly hear, both in his bedroom, so they aren't so bad. The piano I quite like. It's the drums that drive me up the fucking wall.