strange microphonic sound after amp is turned off
Hi all. I am a longtime Audiogoner but a tube amp newbie. I have had my first tube amp for only about six weeks now. Today I noticed something unusual that has not been happening previously. After turning the amplifier (Copland CTA506) off, after about 6 or 7 seconds (as the capacitors finish discharging?) there is a gentle rumbly/staticy sound out of the left speaker. Goes away after a few seconds. Not very loud. Doesn't seem to happen when I turn the amp back on, and music playback seems unaffected (at least so far).
As a musician the thing I liken this to is when you move an ungrounded microphone cable around on stage and you get some sound out of the amp.
I've checked all of the cable connections (power, interconnect, speaker) and they are all fine.
My only other components are an EAR Acute CD player (older model straight into the amp -- use the CD players volume control) and an Audience Adept Response AR-6T power conditioner.
Your advice is most appreciated.