He can test if its the inverter by parking close to his house and runnig a cable from the house to power the pc, but it should not be the inverter if it goeas away with the ignition off.
Inverter should be connected with 2 thick cables direct to battery and dont share them with anything else.
Try taking all gounds to a single bolt through the vehicle floor, and taking power for all your equipment form the battery(+) terminal.
I have had whines were the amps where connected to battery(+) but the HU was connected to the cars electrical system etc, I would be looking at the amps/HU.
^^^ That didn't work, now I'm going to get an isolation transformer from Jaycar...
http://www.jaycar.com.au/productView.asp?ID=AA3085&CATID=24&keywords=&SPECI AL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pag eNumber=&priceMin=&priceMax=&SUBCATID=563
I have a Pioneer MP4600P and I'm installing an xbox for my multi-media device.
This whining problem seems almost specific to Pioneer head units.
If I plug in my xbox even with it turned off into my inverter I will get a high pitch whine if the engine is running or not.
If I unplug the xbox the sound is immediately gone.
NOTE: I don't have my CD-RB20 auxiliary adapter yet.
So what I'm hoping is when I hook up the adapter it will eliminate the whine because it is powered and needs to be grounded as well.
But once again let me state, it's has a whine with the xbox plugged in whether on or off, engine running or not.
I haven't tried direct house power yet, so trial and error will tell once I get my adapter.
'88 Dropped Mini
Try testing grounding resistance with a multimeter to where you ground your electronics.
Have you grounded your altinator in the cars engine bay?
Look by the battery in your engine bay. See the ground wire connected to the car body to the (-) terminal? If that is a 10 gauge wire rusty wire, yank that out and put some 4 gauge and sand the contact points where it connects to the body.