Avionics - engine related static

Over the last year or so I've noticed a gradual increase in engine-
related radio and intercom static in my Grob 103 SL. I've checked the
grounding of the ignition system and I am using R-type spark plugs.
The interesting feature of this static is that I can make it go away
completely if I tug a bit on the airbrake handle (not enough to
release the brakes, just a gentle pressure). Releasing the pressure
causes the static to reappear.

I'm wondering if this pressure exerts force on a bulkhead or metal
fitting that is somehow connected to a ground that has become
intermittent and makes better contact with the pressure. Any avionics
techs out there with advice on how to troubleshoot this problem?