Popping in speakers when radio is in Mute

I  have a 6600.  When It is on and I am connected to it via LAN I get a clicking and popping sound in my speakers  when it is in "mute".  I also can hear some type of hetrodyning at a very low level.  This happens when the volume is turned down all the way and even happens when I "mute" the radio.  Just curious if anyone else has this issue.  I opened a ticket and it was suggested that I do a factory reset. I did reset the radio and it seemed to go away.  Unfortunately it is back.  I am not sure if the reset made it go away or it was just a coincidence that it went away.  I will probably reopen the ticket pending any info I can get here.  I am running 2.4.9.  Perhaps I will try upgrading and see if the issue is still there.  Thanks for any info anyone can give.  HATE to send the radio back, especially for an intermittent issue like this.