TX212 makes an odd buzzing sound.

I’ve tried a number of permutations and get the same result: playing a clear, clean note sounds fizzy, but not like distortion. The fizz follows the note. Like ‘pling..fzzzzz’. It is most noticeable with bass notes.

Variations that I have tried include
Guitar> Vox stomp lab > speaker
Guitar > booster pedal > speaker
Bass > Vox stomp lab (bass version) > Boss RC300 > mixer > speaker

I have also tried a different power source, pushing the contour button and reducing volume.

Any ideas? Is my speaker faulty? What else can I try?
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