This has been a problem for several RR2150 owners, including me. A thread on "static when changing volume" appeared in The Outlaw Saloon as early as January, 2007.

I began experiencing the problem less than a year after having bought the 2150. Neither I nor my wife smoke, and we don' "live right next to the ocean... or have some really nasty chemicals open..." in our house.

The problem can be "solved," but only temporarily, by vigorously turning the volume control knob back and forth a few times.