u/-knotten_

Hi everyone,
I’m struggling with a persistent 50 Hz mechanical transformer hum coming from my subwoofer and could use some input.
The hum has been present ever since I bought the subwoofer new. The seller recently sent me a brand-new amplifier module to replace the original one, but after installing it, the issue remains. The hum disappears for 2–3 seconds on boot, but returns as soon as audio plays or after pausing.
Troubleshooting done so far:
Measured wall outlet: 224V AC, ~12mV DC offset.
Disconnected RCA / signal cables: Hum persists regardless of input.
Tested on different circuits in the house: Same result.
Since the hum is identical on two different amp modules, I’m wondering: Is this just a flaw/inherent characteristic of this specific transformer model, or is there anything else I should check before returning it?
Thanks for any advice!

I bought this new Dynavoice Challenger CSB-V12 about two weeks ago, and it has made this humming noise since day one.
The hum doesn’t come from the speaker driver but from inside the cabinet, seemingly from the amplifier or transformer. I can hear it from over 5 meters away, which becomes distracting during quiet scenes in movies.
I’ve already tried disconnecting the RCA cable so that only the power cable is connected, but the humming remains. It disappears completely when the subwoofer goes into standby.
Is this considered normal for this model, or should I contact the retailer and ask for a replacement?