Rear mech not right - long boring story involving taking it apart months ago, then mixing up the parts with another mech and not being able to put it back together quite right. Own stupid fault really.
Also turns out 3 of the rings on my old cassette were worn so bad the chain was skipping - didn't find this out till last night - was able to replace two of the rings, but not the 3rd.
Close but no cigar, my own stupid fault really, I really left it too late.