By SMPS source I mean that the only wiring between the bike and your kit is between the bike's battery and an SMPS dc-dc converter 16-12 volt if that's what your kit runs on. If they put your kit in metal boxes and ground the chassis, then you make sure they are isolated from anything metal (ground) on the bike and rf decoupled with capacitors.
The only place where you need to use the bike metal work as a ground is the antenna. If they are mag mounts then they may already be fully isolated with internal baluns, or unblanced and capacitively coupled to the ground plane, if they are not then you can isolate the screen with capacitors.
In other words, if you measure the high ohm resistance between any part of your comms kit - metalwork, connectors, antennae, - there will be no resistance reading to the bike frame or battery, therefore no ac/dc ground loops.
All stock stuff for hams running mobile rigs.
As for rfi, after eliminating for ground paths or testing with a mains supply and kit isolated from the bike, you just need to break out wifeys aluminium kitchen foil and do some experiments.
The furthest most go will be adding audio kit to bikes, so I would be surprised if you will get quality replies covering tx/rx comms installations. In the past I've found no two installations and problems require the same solution. A lot has to do with understanding interference and some of it is 'Black Art' and not science that can be answered easily in a few posts.
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