What may cause a high pitch hum.even when muted or volume turned down?

Hello there!
Sometimes High pitching its just that, static on the area, like if you are near a microwave, or near other electronic equipments, but, if the skreetching sound keep going or even if you do nothing it could be a line inside the sound card, or you need to clean the volume botton with special electrical cleaner. other that these, its contacts, or bad cap for the volume board inside.
Good Luck!
Carl

this may be due to bad power supply

Not at all in this case. You either have a loose wire to connections to the cartridge, which can be fixed by hand. Just push the wires on to the cartridge. Or you have a fault in the power supply of the deck. Most likely a mains filter capacitor that is letting the 50hz mains hum in.

The hum will either be caused by a poor earth connection or a power supply problem. The stylus would not cause any hum at all.

do u have the unit earth grounded? sounds like AC hum, most amps have a ground lug, make sure that is grouned and the power plug to o the amp has a good ground.

Change the audio amplifier ic are fried

press down and hold the power button for 10 seconds.

This is GroundNoise from the TV's Backlight.

Sorry, but unless you are a Technician, you will simply need to ignore it.

If you are a technician, you can fix this by grounding the Audio ICs to the Power Supply (details not provided)

change the power supply capacitor

Push both volume buttons at once to turn Mute off. You should hear two beeps, ascending in pitch to indicate mute is off. If they go down in pitch mute is being turned on.

The high pitch squeal you hear is usually caused by a coil vibrating, normally in the horizontal circuit. I've also seen the ferrite bead on the horizontal output transistor do this, but, it is rare. I normally will repair this by finding the coil and "tightening" it. To tighten a coil, technicians use different chemicals, such as, a hot glue gun, rubber silicone or even finger nail polish. I will find the coil that screams by starting with the usual suspects and using a wooden dowel, barely touch the coil and if the pitch of the noise changes, then, thats the coil that needs repaired. If you do not know your way around the inside of a television, I never recommend you do so, since, this procedure must be done with the set turned on and you poke your hands around the inside of the set by the high voltage circuit. Hope this helps your decision.