Audio Systems: Subs humming, ac voltmeter, gmc jimmy

Question
How do i get my subs to stop huming when i start my GMC Jimmy. they were all fine till one day i started it and they did nothing but hum. I have rebounded and repowered them to a different source and still same thing.  When I use the audio cables and jump from another Cd player in someone elses car they are fine.  I have switched audio cables and still same thing.  So i know its not the amp i have even switched cd players and still get it.

Answer
Re-check all power connections. Especially the ground. Be sure that all paint is scraped away and the grounding point is shiney metal.

Also be sure the gain or level control is set right.

The purpose of the gain is to match the signal volts RMS coming from the source (CD player, etc.) to the input of the amp to prevent clipping (damage by over powering).

Here is a guide that will help you set the gain correctly http://www.datafilehost.com/download.php?file=6d26c621

You'll need a multi-meter (AC voltmeter), Microsoft Excel and a way to burn an audio CD from an MP3.

If you don't have Excel, use this link http://www.box.net/shared/nkkw1dhk4g