Very good info here. I hope everyone reads and heeds.

Just to add my own two cents... Always perform range checks with the engine running. Almost every glitch I've had with my plane was due to vibration. Most of the glitches wouldn't have shown up with the engine off. Normally it's a new plane and it's something contacting the antenna or just too close. Relocating the antenna has usually solved the problem.

As Fastsky mentioned, sometimes it's just something that's loose causing metal-to-metal contact.

What always bugs me is when a guy at the field has a problem, can't locate it, the problem seems to "go away" and then he flies. Obviously, it could be something as simple as interference that really is gone. But just as obviously it could be something intermittent in the airframe. It's worth taking the time to go over every possibility and rule out anything and everything just for safety and peace of mind.