octave switch noise problem

i was wondering if this was a common problem.

the octave switches (osc 1 and 2) on my RME have become noisey and glitchy, even though its only two years old.

i frequently get a kind of warble effect as i switch octaves, sometimes just momentarily, other times it lingers for a second.
osc 3 is fine, so i presume the switches are going wrong,

anyone else had this happen ?