The ideal way to do the VSWR check is to pull the box and use a tester with an integral signal generator that can be plugged intomthe backplate co-ax socket - HR Smith 12-602 or similar. If this isn't available, then a Thruline watt meter can be installed into the cable behind the rack and you use the radio to generate the test signals. On the TB, Ithink there are disconnect plugs that allow the radio stack to be removed so this is where the in-line wattmeter wil go.
Defective bonding of flying controls or poor static wicks can lead to a build up of static on parts of the airframe when airflow is present, and the static build-up can vary with humidity. When it gets really bad, the squelch on VHF can open on it's own just on the electrical noise! it can affect different systems depending on the relative position of the associated VHF antenna to the noise source.