Radio in my 2017 CRV makes a high pitch frequency sound only when I turn the A/C on. When I turn the AC up to full blast the noise gets louder then disappears. I have had several mechanics check it out and they cannot find any electrical issue. Any ideas? I have a cousin who is a mechanic but I don't want to bother him if nothing is to be found and the real reason is a defective radio?

 

have your cousin check the fan motor for high pitch frequency sound.

 

A high pitch sound that the blower motor makes on the radio??

Could be a few things causing this
One ... is the blower motor or controls are feeding back this high pitch frequency on the electrical lines?
Two ... the radio is not functioning properly and doesn't filter out noise on the power line?
Three .. there could be a possible short somewhere?
Four ... the grounding is not good enough to prevent the feedback to the radio?
There might be something else but these are the ones I thought of

Some possible solutions could be to clean up the grounds?
Or put some shielding on the wires?
Or put an electronic filter on the power line to the radio?
Or replace the motor and/or the controls?
Or replace the radio?

Of course, I would never take my advice because this is only guessing
There should be someway to test this by using an oscilloscope