Good luck getting this fixed. I have had this SAME problem on my 2010 Equinox since I bought it in august of 2009.
It has been to the dealer at lest 16 times. GM has had case numbers pulled on it only to be told by the dealer that they can't duplicate the problem. I just took it in to the dealer just yesterday 8/30/11 with a non working Nav system/radio no sounds it was witnessed by the service consultant but he could not get a tech to look at it at that moment. I left it at the dealer and of course this morning when the tech looked at it they were unable to duplicate it.
The service consultant said the tech needed to verify a couple things before they could order the parts to fix it because Chevrolet would not replace the part without the tech seeing the problem firsthand. (I have recorded several of the instances on video)
Wow, you've let them have 16 opportunities to fix this? It's so frustrating that they have to witness problems like that, I mean it makes complete sense that they have to witness it, but I would say if it's been happening for 2 years and you have VIDEO PROOF of it, they would believe you. You might need to try a different dealer, I'm surprised they haven't fixed this yet for you, or even offered to replace the whole nav/radio system in an effort to fix it. You might start requesting that. I would be beyond frustrated at this point if I were you. Hang in there, hopefully they'll fix it this time.