Bought FP5 used; been enjoying it for about a year. Once in a while, the sound would be raspy/harsh/echo-ey, then clear up. Getting progressively worse. Sprayed contact cleaner onto volume knob and problem went away. No more. All the time. But if i hammer a note for a few minutes, problem goes away. On all outputs including both headphone jacks. Does it on demo songs and if I use external sequencer and midi input to keyboard. Opened up unit and sprayed contact cleaner on circuit board; went away and then came back on any voice. Any ideas?