Some units are more affected than others. If there wasn't a problem then Yamaha Japan wouldn't have shipped parts to the USA to repair my NP-30 and others who have reported the same problem. My unit will be shipped shortly for a warranty repair.

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.