We are having a strange problem with our set of Audio Technica 1800 series wireless lavs.
It seems as though the amplitude of the sound is jittering up and down by a few db. It throws the dynamic of the vocal and makes it difficult to listen to. It sounds like some awful auto-gain.
Incidentally, sometimes there is white noise that comes in and out with the vocal - kind of like room tone when you have an expander on too hard.
The buildings we are in do tend to have a lot of wireless devices transmitting and receiving but we've tried changing frequencies a few times to no avail.