The active speaker is ringing in human speech, what should I do?

Question

Do it yourself

Speakers Sven, they are 10 years old. The amplifier is analog, on one of the standard five-legged microcircuits. The tone block is digital.
The active speaker began ringing at certain frequencies - mainly in human speech. Who to blame - speaker, amplifier, harness? How to diagnose and is it worth repairing?

The speakers were being repaired - after the move, a 50-Hz noise was discovered, it turned out to be a transformer.

UPD. While suspicion on the aluminum chassis of the amplifier.