Tom,

If you have a grounded lightning arrester in the coax line, and if you 
are using a 3 prong AC line cord on your power supply that is 
connected to a properly grounded outlet, you should already be 
grounded well enough for safety and lightning.

So, here is a cheap trick for stray RF. use a quarter wave 
counterpoise wire. Just do the math for a quarter wave on whatever 
band or bands where you have a problem. The math you work is 234 
divided by the frequency, such as 7.150, 28.400, etc.

Cut a piece of just about any wire, even cheap speaker cable, to that 
length. Strip enough insulation off one end of that wire to attach it 
to the ground screw on your rig, or to the ground of the tuner if it 
is separate from the rig. Then, route the wire wherever it can be 
routed in order to stay out of your way, not be a trip hazard, and not 
be something your dog or child might mistake for a chew toy while you 
are transmitting. A quarter wave is broad banded enough that you won't 
have to worry about pruning the wire beyond the length the formula 
gives you. You can connect these wires for multiple bands, but more 
often than not, one wire cut for the lowest problem band will solve 
the problem on the others as well.

This is much cheaper than anybody's "artificial ground," and serves 
exactly the same purpose. I laughed when somebody told me that, then I 
added a 40 meter counterpoise to the end fed zepp I was running from 
my second floor apartment. The way it improved the performance of my 
antenna tuner was almost magical.

You indicated that you are hearing a hum on your signal. RF on the 
signal generally appears in the form of distorted audio rather than as 
hum. If hum is the issue, you probably have a poor connection on the 
shield of either your microphone cable, or on the cable of something 
that is plugged into your rig. The only fix for that type of hum is to 
repair the cable.

Hope this helps.

Mike Duke, K5XU
American Council of Blind Radio Amateurs