Loud hum in audio system

Hi all. We have a problem Huston! When we 1st bought our van back in 2004, we noticed a very loud hum coming through the sound system speakers especially when the sun was on the solar panels. Anyone we asked advice from ,said to place a 1000 microfarrad capacitor between the circuit breaker and the neutral link on the auxillary breaker. This seemed to solve the problem for a number of years, but lately since we have installed the new digital tv, the noise from the speakers has returned with a vengeance. Sound In Motion sent us a lead to plug into the existing leads which then plug into the tv, but it has not solved the problem, and to be honest, I don't think they really know what the solution is! Does anyone else know what to do or can they shed any light on the subject? The noise is almost drowning out the sound of the tv! The other half is in the process of testing the capacitor to see if it is still ok, but he is now back at work for the afternoon and I won't know what the outcome is until he gets home later tonight. I need advice!!!
Regards, Jan O