Microlab A6662 beeping speakers?

Question

Electronics

Microlab A6662 squeak in the speakers when the front panel is connected, I turn off the control panel, everything subsides, what can be?

Answer 1

the dumbest thing is to put the capacitance on power to protect against interference.
a large electrolyte for low frequencies and several ceramic ones for high frequencies.

Answer 2

The issue is resolved: over time, apparently, the tanks degraded (after all, they stand around the UTC7805 - the tanks got hot and dry), and the ripples get into the power - I replaced the capacitors around the UTC7805.