Problem with 2004 Pontiac Grand Prix car stereo

The treble, or high end, cuts out intermittently when I'm driving, or idling at a stop light. I've taken it to the dealer at least three
times in hopes of correcting it. They replaced the radio itself, yet the problem persists. Furthermore, they could not "re-create" the problem - so no action was taken. Apparently this is typical, no wonder GM is losing market share.
Rather than take it in a fourth time, I have opted to take it to a car audio shop to fix it. At this point, with the less than satisfactory service from the dealer, I am ready to pay for this problem to go away. Anyone else have the same issue?
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