In octave four a couple of notes play loud

by Sandra Waldron
(Milton, Wa USA)

I have a Yamaha YPG 535 that my son purchased for me back in October for my birthday.

I have two questions. One is-- in octave four I have a couple of notes that really stand out when I play a chord. How can I fix that?

Second one -- And I know it's not a big deal, but why does the manual say to unplug piano when not using because it is connected to electricity. So are many other things in the house, and they aren't unplugged when not in use. I can see the possibility of someone perhaps spilling something on keys, but I have been a pianist all my life, and am very careful with food and drinks around any piano, digital or not. I have been unplugging it, since I read that. But I would rather just leave it plugged in, as I often sit down just for a few minutes between doing other things, and I had to have to keep plugging and unplugging it.

First question is the most important one, though.

Thanks in advance.