Hmmm never heard of that problem.. It might be the disk. Did you try to do a factory reset? When I had the PSR-540 I never had a problem like that with it... I suggest trying another disk. I did have problems with disks when I used the 540.
Squeak
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.