Buzzing bulkhead

Hi all,
'53 TD5 has buzzed since owned (7 months). Only happens under load and appears to come from the dash area. Garage attempted to fix but broke the windscreen while trying to get at the bulkhead. Don't know how and didn't hang around to ask.

I'm convinced that it's on the engine side of the bulkhead but don't know where to start looking. As it only happens under load I can't stick my head under the bonnet to find it!

Any ideas? I'm not a great mechanic but can handle a screwdriver and hammer!

Cheers.

Sorted it. U clip on the air con pipe (I think) attached to bulkhead behind the block. Pulled straight off as the nut had obviously worked loose and dropped off leaving the thread to vibrate against the head causing the vibration/buzzing.
Bliss.