Welcome! If it hasn't had a valve adjustment then it's long overdue, so it could be your noise. Hard to say with no idea what sort of noise it's actually making. I've never had a bike with a fuel gauge, so I don't know how they work but if they're anything like a car I'd assume the rust that was in your tank may indicate a stuck float or something. Sounds like it probably sat for awhile. Anywa, I think overall the ZX12 has proven to be a fairly reliable machine, but more importantly you don't see them much. I think they will come to be highly sought out by those people who aren't in the new bike market, don't want to have to taxi a big ZX14 around and aren't comfortable on an aggressive 1000 class. Post some pictures! Good luck with it.