knocking

Hey all I've just put a new set of Hairpins on my 200, and wizzed down to the local tyre place to get a puncture fixed on one of the tyres. They also pointed out that one of the tyres was worn down on the inside edge so I got that replaced while I was there (now on the rear left). They also...

Sorry in advance for the long post, want to make sure you have all the info for this one. So I pulled into tesco petrol station at about 2am this morning. Realised after I opened my window it was making a new noise... not a good one. Popped the bonnet and had a look. It was a sort of rapid...

Right, i thought at first it was the balancing, as the knocking is very rythmic and seems to be consistant with the speed. After being to the tyre outfit the other day they confirmed everything is in order so i can rule out the wheels. i hear no knocking at very low speeds nor anything...