Metallic vibration noise behind dash?

[sam4191]

I have a rather odd metallic sounding vibration noise, which seems to be coming from behind/under the dash.

It only happens at between 4,500rpm and 5,000rpm, so only when i'm accelerating hard.

Does anyone have an idea as to what this could be please?

 

[dieselfitter251]

erm...embarresed to admit this. I had a similar noise. In the small dash box (to the right of the switches) with the flip lid I'd left some coins... and sure enough, that was the vibration!