There are several posts on this problem. Yet does anyone read all the threads? Unlike other "know it alls" on tis forum - I don't truly know the root cause, I only think I know. So as I noted in previous threads, has anyone tried blocking the rear speaker? For example, take a towel, fold it, and block the rear speaker (near the rear hatch back), then get something heavy to hold the towel against the speaker - then bungee it. After the speaker is muffled, then report whether or not the bass sound goes away. In my case it did. I will bring my new GCL to the dealer when I need my first oil change - in a few weeks. Now that I have muffled the sound. I can live with the problem (that's artificial gone) for a few more weeks. Here's what I think I know, the noise activation system has an issue. I am hopeful a future firmware or software fix will fix it. The next step for me (if the dealer can't fix it)? Remove the rear speaker and cut the wires. Oh, and by the way, with the rear speaker muffled - the Macintosh system still sounds incredible - bass and all.