Great Planes Pitts Glitches
If you are using *ANY* Brand on straight FM (not PCM) this is VERY likely. And very dependent on antenna positions, both of the receiver and the Tx.
Range check it thoroughly and have a helper identify any twitches AT all. Use the 'walk a circle' range test, if your facility has the space.
For years, if there is no metal-to-metal I have very successfully flown straight PPM FM of several brands with no issues.