Thanks @Al-2.0 They look very similar to the ones I posted but probably a better quality. Can I be a bit pedantic, as I only want to take the heavy machine off the wall once. Did you go for an M6 size with 50mm length and use a cheese head screw (it is not clear how much clearance there is between the bracket and the machine for say a rubber washer plus bolt head)? Did you also have a rubber grommet on the Victron mount to reduce vibration transfer?
At the moment, using your information and that from @B51-technician , I am intending to remove the transformer and put a rubber isolation pad behind it, install the Rawl Flexi Plug, with grommets and cut the edge of the fan to stop the power cable being squeezed between it and the case.
I am hoping to be able to remove the strap to stop the enclosure from vibrating, but I doubt that will be the case. I have already glued sound proofing to the back of it.
In answer to your question @B51-technician my serial number starts HQ2315, it is meant to be quiet but it is far from being that.
Like others I struggle to understand why Victron would spoil a great product by not taking some basic measures.