Strange Compressor Behavior

I bought a DBX 1066 as partof a wider studio upgrade, and I'm noticing unusual behavior. There's intermittant noise, unexplained changes in sensitivity, gain, and compression, and this:
 

 

 
As the pics show, the 1066 meter shows a -3 to -6 db signal on the left channel, regardless of output gain or meter switch settings, and further, no corresponding signal on the upper MOTU 2408, analog channels 5 and 6, where the 1066 is tied in.
 
I have MOTU 1 analog 7 and 8 outputs jacked into the sidechain returns, but there's no signal showing on MOTU 1 7/8 either.
 
Since taking these pictures 15 minutes ago, the indicated signal has disappeared, without any action on my part. I can make it go away by power cycling the unit as well. There is never any audible effect or indication of this signal in the MOTU's CueMix software.
 
I'm going to ping DBX support this week, but wanted to get a sanity check here in case this is easily fixable or something dumb I'm doing.
 
Thoughts?

Good idea.
 
Pulled the returns yesterday, no joy. Just pulled the ins, no joy. Pulled the outs, joy. Outs back in, with no ins, no joy, non-signal re-appears.  Plugged the ins back in, "signal" disappears. It'll be back.
 
Thanks!