Interference from power inverter.

I have that same inverter in my Work Van...I use it to power a full size refrigerator. I also run a 2x6 amp with my radio, and do not notice any noise related to the inverter or any other electrical devices...The radio sounds the same whether the motor is running or not, or if the inverter is running or not.

It maybe caused by how you have your inverter wired...In my case, the inverter is wired to bank of 4 battery's, and then there's a cable which runs from the bank back to the starting battery under the hood for charging the battery bank.

Just guessing, but I think if you do some bonding ( or RF Grounding) for your radio equipment you can probably eliminate your noise problem...I would also check how you have your coax ran. If it's too close, or touching power cables it may be picking up the noise that way.

Bottom line...saying "there's nothing you can do about it, is bunk"...Just depends on how much time you want to invest in getting rid of the problem.