Got my first ever Scooby (sti9 on 54 plate) this Friday

CEL came on (solid) after 70 miles or so, on Saturday
Was only doing 3krpm (less than 80mph) on M4, when there was "thwack", but no discernable loss of power.

Starts fine, idles fine, seems to want to spool ok (but I hold off after 3500rpm)

It does have a wrc-tech ppp 350 mod, and reading some of the threads/sites would appear the CEL coming on is not terminal

Drove back the 60 miles or so at 65mph, but haven't driven it since.

Any ideas/comments etc would be really appreciated........
Thinking of getting OBDII reader of some kind, and like the look of the auto-enginuity software, any good?

Thanks in advance for any help