Odd transpose changes happening on Alesis Q6.2 synth
I've had my Q6.2 for a year or two now, and several months ago began noticing something which has become progressively worse as time has gone on. While playing, the key will be transposed up or down and then back randomly. Sometimes the transpose lasts for a split second, sounding more like a "flicker" in the sound, and other times it will last as long as 20 or 30 seconds before reverting. I've tried going back to factory settings several times, but this hasn't helped at all. The pitch bend isn't dirty or dislodged or anything, and it's much too great a transpose (often an octave and a half or more) for it to be that, anyway.
Is there any way to fix this, and is it a common or known issue? Thanks very much.