I recently acquired an old Magnavox FD3030 (Philips CD303) CD player for very cheap advertised as non working. After pressing the play button over and over again it eventually played a CD and worked fine for about a month. Now it's emitting a 120 hertz hum through the line output for about 30 seconds after turning it on then it stops. It doesn't matter if there's a CD in or if the motor is spinning, it will hum for about 30 seconds then stop. If I turn it off and back on it won't hum but if I leave it off for a while it will so it seams like once it's warmed up it works fine. I already replaced all the caps on the power supply board with new Panasonic FM caps of the same value. Does anyone know what else might be causing this problem? Any help would be much appreciated.