noises at low revs but not at idle

[jonnybumps]

Over the last 20 miles I have developed what sounds like a rattle from the engine bay which has got a little louder as I drive .
I had presumed that it was a piece of heat shield or something similar . However having taken the front and rear covers from around the engine the noise seems to be coming from the front of the engine at the top .
It only does this as you pull off and not when at idle - once driving on the road it seems to go or at least gets a lot quieter .
No obvious change in performance .

Any thoughts ?

Thanks Jon

[jonnybumps]

m4tti said:

If you can, remove the can cover and see if there are witness marks from the chain hitting it.

I will do this after work today - It sounds like the chains hitting the cover to me - I will report later .
Thanks for your input .