Hi this sounds very off, indeed.
Are all the other functions (normal playing, arpeggiator, etc..) working correctly? Has this issue been there from the very beginning, or did it occur after a while?
Did you have midi in and out unplugged? Could be there is some kind of midi feedback issue here..
The Voltage is not too low for the processor to work, but I would expect a detuned sound, because it is also the voltage that drives the D/A converter..
What you could try, although I don’t know why it would help, is to update the firmware: