Meridian 556- Buzzing relay

Hi everyone
I urgently need your help on a Meridian 556
It plays normal without any anomaly except that if ever I switch off the pre amplifier before switching the Meridian 556, then I get a loud buzzing (vibration) coming from the relays. Whenever I switch back the preamp, the buzzing stops and the Meridian plays ok .
What could be the cause of this problem
ThAnks
Regards
 

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I recently purchased two Meridian 556 amps and I am getting a fluttering sound from one of them after a few seconds of being powered up. It sounds like the a relay is opening and closing rapidly, and it happens whether or not there is a source playing.

Did you ever find a solution to this? I got these amps for not a lot of money, so I'm not really upset about it, but I'd like to get a handle on it before I kick off a full recap.

Thanks