wrote:

Go to an avionics shop that knows how to properly install a metal backing
plate in a fabric aircraft.

My AI and I installed a backing plate under the TXP antenna about a year
ago. Prior to this, it was mounted only through the (very thin) aluminum
boot cowl, and was very flexible. I'm guessing that adding the backing
plate stiffened the mount to where the whip now hits some vibration
modes excited by the propellor pulses...

Ask how much to replace the existing antenna and how much to move it back.

No expertise with fabric aircraft at any local avionics shop. The
replacement antenna TED 12-10 can be had from Spruce for $20, Chief for
$23, and eBay for $15+