Have an '89+ equalizer radio without the search button for the tape deck.
Was testing it on my workbnch with a power supply and noticed that it was making beeping noises about 3-4 times a second when the volume was low and seemed to go away after I turned the volume up

Tested this on an identical '89+ deck and did the same thing. But then tested with an '89 deck with standard treble and bass and no problem. Whats could be wrong? Is my power supply not strong enough (lights dim when playing music) for the equalizer decks or is there something wrong with both equalizer radios?