[W8ZV]

Part of the issue with BOTH of these units has to do with grounding, bonding and power source balancing (read AC power source).  I have an SS3000.  Depending on what I have turned on and off in the house, the background hum goes up and down.  It's a power line balance issue.  Second, the grounding for the antenna has a LOT to do with the hum on the signal.  It's same thing we hams fight on AM on the ham bands.  Grounding and bonding issues introduce hum on the modulation signal going to the transmitter.  If your input signal is noisy, the transmitted signal is going to be noisy.  SO, you listen to your own signal on a second receiver.  IF you have GOBS of hum, then you go looking for a grounding/bonding/shielding issue.  You can also have a BALANCE  issue.  Check for AC voltage on the input lines.  IF you have an AC voltage floating on the input lines (you need a scope to find this), you need to isolate the grounds between the feed and the transmitter.  Getting CLEAN signal to an AM transmitter is NOT as easy as it looks.  This can be a project, depending on the building (read house), the age of the AC service, and the other mechanicals (plumbing, HVAC/R, ductwork, etc) present.  LOTS of things can present issues that take some time to troubleshoot and eliminate.  IT CAN BE PHUN!!!