I've been having troubles on and off with losing one or both of the front speakers in my Silverado. No popping or cracking or anything that sounds like a speaker going bad. And when they do start working - they sound good as new. I've never any problems with the back speakers. Recently I've noticed that when I drive the truck to work in the morning, the front speakers are out. When I get back in the truck at the end of the afternoon, one or both speakers are working. Dampness? Bad ground? Any ideas?