I Installed my carputer setup using an IBM Thinkpad T20 Laptop and 7" Lilliput Screen. I have the stereo connector plugged into the aux port on the back of my HU. I used a VGA extension cable to plug in the Lilli. The system works great except for this noise issue. I know there are hundreds of posts about this issue but none have been resolved completely. I was hoping some experts could help me troubleshoot and fix this problem.

The noise I hear ONLY occurs when I have the laptop plugged into the DC-DC converter that I bought off ebay. The converter is connected to the same 12V cable that runs from the battery to the amp powering my sub. The converter is also connected to the same ground that grounds the sub. The ground wire is very short and goes directly the seatbelt bolt in the back seat.

Moving the converter while it is plugged in, toward and away from the laptop makes no change in the static. This rules out any possibility of the noise coming from EMI but just to be sure I tried somethign else. I tried disconnecting the power converter and connecting it to another IBM laptop. As soon as I do this and even after the other laptop is being powered, the audio is crystal clear coming from the original laptop running off the battery. Wrapping any cables in tin foil is not going to fix this problem.

I read a post that suggested buying an external USB sound card. I thought this may work as maybe the internal soundcard might have a grounding issue when the power is connected. So, I bought a Creative USB external sound card. This had no effect on the noise. It is powered by the 5V that the computer runs from so maybe the noise just comes through.

I have read about ground loop isolators but I'm not sure it will entirely fix the problem, It will probably just mask it. Also I have heard that they reduce the quality of the sound.

Is it possible to run the USB sound card off of a seperate 5V power supply by tapping into the wires?

What about buying a power inverter and then using the AC-DC converter the laptop came with?

I have read about grounding the computer's chassis but I haven't read about one person that has reduced the noise to an acceptable level.

Has anyone had this happen to them before and fixed it?