All of a sudden my subwoofer has developed a hum.I disconnected the cable and it goes away.I replaced the cable and it is still there. could it be something in the 990?the 990 is plugged into a power center with line conditioning. It is a new problem it has been fine up until now.

Hi Evan,is it the rca cable or the power cable you are talking about? have you tried a different rca cable?

its the rca cable

Check the route of the RCA cable to see if it is running parallel to a power cable or even a speaker cable for a significant distance - if it or some other cable has gotten moved somewhat recently, there could be EM interference (caused by the closer proximity) creating the hum.

The hum is only present when the 990 is on. If I turn the sub on by itself or disconnect it from the 990 the hum is not present. I tried it hooked to both sub outs and the problem is still there. I even hooked a filter for groundloop hum to the rca cable of the sub and it did not help.The problem to me is sommething comming from the sub output of the 990.

OK my hum is gone ,I tracked it down to the cables between the 990 and the sms1. New cables and no hum