I'm new here but have found the forum well useful.
Just started an install yesterday of Toughbook CF28 running PowerDVD 5 connected through a CD changer adaptor lead to my Kenwood KDC-PSW9524. All was well running off the laptop battery. Then I connected up my Nikkai 300W modified square wave 12 to 240 v inverter. Humming like mad...
Did lots of browsing here. People saying use DC-Dc, and ditch the inverter, people saying inverters are crap and inefficient, people saying inverters will wreck the laptop, move the leads and all sorts. I had already set my mind on the inverter though as I need 240V to power my 17 inch TFT screen that's going in the rear of the bus. And the inverter will be useful for other things.
The inverter is properly grounded as is my head unit. Almost went and bought a plug in surge protector as that solved someone's similar problem a surge. So I decided to try the same set up but with the inverter plugged into my 12v power pack instead of into the ciggy lighter. Result - NO HUM. Got to be an earthing issue - so I grabbed a bit of wire, connected it to a screw under the dashboard and touched the other end on the outside of the RCA plugs - Hum all gone.
I've now earthed the RCA soskets on my leads by lockwiring the outer of the red and white together, and lockwiring the core of some 8 guage earthing cable to it, soldering it and then potting the whole lot in epoxy resin with the connectors on the RCA sockets still accessible. The whole fix cost me pennies when I was on the verge of splashing out mega money on a proper sinewave inverter.
i've now got a nice set up. Just need to work out how to mount the Toughbook on the dash of my bus!
Moral - bad earth is the cause of many problems, don't forget it!
Pete, Brighton UK