i recently bought this receiver (JVC VCR-5501) fairly cheap and it works fine and sounds good, but when its left on for about an hour or so it starts to make an oscillating humming sound through the speakers and gets louder as its left on. it only goes away when it is turned off and left off for about 15-20 mins. Is this normal? If not, how can I fix it? (it is not a ground hum. It is grounded properly and hums much louder when it isnt.)
