Quote Originally Posted by MalGib
Let me set the scene ... accelerating in 2nd gear, upward incline in the road, as the tacho passes 3500rpm ... clickity-clack clickity-clack from the engine ... change to 3rd ... noise stops. My Euro does this every now and then, but not consistantly ... when it does happen though, it's nearly always in 2nd gear, on an uphill run and when the revs get to about 3500 rpm and above.
Hey Malgib I just remembered something. A long time ago I noticed I had some vibrating sounds under the bonnet (only at certain RPMs and only from time to time). I discovered that the fuse box lid was not on properly (above the air filter) and was rattling. Check that and your air box screws.

And do you have an Icebox? Sometimes I get some vibration sounds from that too.

I think Aarong is right re pinging - it would certainly be unusual if you are using 95 ron. Maybe if you were using 91 ron but not 95.