New zx7 knocking when warm

Hi,

I've just purchased a zx7 97 P2 I think. it has 29k with no history.
On first inspection the bike seems and rides fine but today I have noticed something I don't like.

Riding the bike normally with revs under 5k the bike sounds like a zx7, if I give some beans and rev over 5k (Only when warm) I can hear a knocking/thumping noise from the engine. It seems like its coming from the front of the engine. Also and may not be related its happened a few times, it seems to pop/ping one big noise like exhaust backfire but comes from the engine. again this has only happened a couple of times.

I have changed the oil, 10w40 semi, new filter. it was missing the top cam chain guide so fitted a new one. looked like it had been hitting the top studs.


Anyway, Any information you can give me would be great. Anything I can check myself to keep the repair bill down too.

thanks in advance.
Paddy