Metal ticking problem

I have a mk1 Golf with a G60 Rallye engine

Symptoms: A clicking or rasping noise coming from the engine bay area. The noise happens when the car is in motion and increases in frequency, as in it happens more often, as the car accelerates and gets louder as the car gets hotter.

Fault investigation: Knowing I've had a pretty shagged exhaust for a while I found a hole in it, so changed it for a nice powerflow one. However, the symptoms are still apparent. My car was coming up to a 10 000 mile service, believing the noise might be a pressure control valve from a clogged filter I changed the oil, oil filter and fuel filter. Symptoms still apparent. My car has been over fuelling, so I thought I was in no danger of pinking, but a friend of mine said that was not the case. I removed one of spark plugs to get it replaced. It was a NGK BP7EVX, and it was caked in oil and the end was black and looked burnt. IS THIS NORMAL? The NGK spark plug is platinum, which is what the engine requires, but has a gap pf 0.8mm but the Bentley Manual for the Corrado G60 engine suggests a gap of 0.6-0.7mm. So I've ordered some W6DPO, as the manual recommends, at over the odds prices.

I'm obviously a little concerned about oil in cylinders and would appreciate all advice with what I can do.