Electronic volume controls

I have several different models of stereo amplifiers with electronic volume controls. They all have the same problem. when you turn the knob up or down the volume drifts randomly. These are not potentiometer controls so I am at a loss as to how to proceed. If the ground leg were off on a "normal" volume control I would expect that effect. Any suggestions would be appreciated.

They are most likely rotary encoders, and their contacts are dirty - you 'may' be able to cure them with switch cleaner. Or failing that, replace them - but you probably need to source the encoder from the equipment manufacturer. It's simply that the dirty controls provide a random array of noisy pulses, instead of the nice clean ones.

Thank you for the info! I now know also what their proper name is. This seems totally logical.