I've got a problem with a Privia PX-770 purchased a year ago. The C4 and C5 keys (and only these two) produce a "weird" very unpleasant sound.
Compared to other keys they sound resounding and droning. Here is a short demonstration video:
https://youtu.be/Ds6j6uMKbQU
Is there any way to fix that?
There is no issue while playing using headphones.