popping noise fron usb flash drive

Hi All, New to this forum, but not new to stereo installs. I've always had decent to high end audio equipment in my vehicles, but I've run across something I've never seen before. I recently installed a Pioneer DEH-X8500BH, with a couple of amps. I amp is for my Sub, the other a 4 channel for my mids & tweets. It sounded great for the first few days, then I started getting static type pops when listening to my jams off a Sandisk 8Gb Flash drive. It sounds like all my music was recorded off of albums with scratches. At first I thought it was electrical interference from my Vans electrical system, relays clicking and so forth. I also have a Sandisk Fuze+ music player which plugs into the 1/8" jack on the front of the unit. When listening this way, no pops or clicks what so ever. There is NO popping or clicking with FM either. I've been reading here for several weeks, and done extensive Google searches for this issue and all I can find are iPods that are hooked into a car audio system using USB, having the same problem. Although they solved their problem with a simple firmware upgrade to their iPods. I'm not new to car audio or the proper way to hook up power, ground and speaker connections. I used the recommendations from here and Crutchfield, to insure proper installation, and had it looked over by a local Stereo install shop, he concurs I've got my connections in properly. He's heard of other people getting popping sounds from USB sticks, but has no remedy. I'm going to buy a couple of different brand Flash drives today and load some music on them, just to see what happens, but would really appreciate any tips form the forum. Thanks in advance - Gadgetman728

2000 Astro Cargo van. Pioneer DEH-X8500BH Head unit Pioneer GM-8604   4 channel amp Fosgate Punch 2 channel, bridged to 1 channel for Sub. Fosgate punch 12" sub 2- JBL GTO938 6 x 9's & 2- JBL GTO638 6.5-Inch 3-Way Speakers for the rear. 2- Polk Audio db6501 Component Speakers for the front. The Fosgate equipment is used and dated, all the rest is BRAND NEW!!

I bought a 32Gb. Sandisk Flash Drive from WalMart, loaded 10 gigs of music to it. It played flawlessly for about 1/2 hr. then it started doing the same thing, static popping noise. 38 views and no ideas.