Korg Prologue Troubleshooting

I have a relatively new Korg Prologue 8. Recently it has an issue where it “crackles” loudly just as I press a note. Then it goes away for the sustain of the note. It doesn’t happen every time. Probably 50-60 percent.

Now it continues to have this problem and also sounds very bright. Too bright. Shrill even. Far more than originally on the same patches.

I don’t know where to begin to troubleshoot.