Truma trumatic heater rattles

Check the pipe runs once the cover is off, you may find 2 pipes actually touching or have sufficient play in them to touch. These can be separated using pipe wrap from B&Q. A company called Noisekiller may also have a heat proof pad for the inside of the cover which can resonate on the move. I used their anti noise paint on the inside of our heater cover but its now discontinued.
On a lighter note you could consider driving in Norway- all our Executive rattles disappeared on their roads (except the ones with the tops ripped off for repairs) !!