I have an 03 Z71 Tahoe that I purchased a couple of months ago, and I cannot seem to figure out why the front 2 door speakers work fine but the rear 2 door speakers just barely have any sound coming out of them...It has a factory deck now, but I figure the guy before me had an aftermarket one because I have 2 sets of tweeters (which only the front work), and some RCAs tucked away under the dash... My XM won't work either, but I would rather get all the speakers working first.. Anyone have any ideas???