Could be water getting into the ground contact points along the chassis. That can cause tons of random electrical issues. You should go to the dealer and get them to inspect it, and mention that it happens after washing the car.

 

I've had a similar thing happen with a head set that I have. It will work with my Motorola for a couple months and then I will have connection problems.

I delete the headset from my phone, turn off the phone and turn it back on and the problem seems to stay away for a couple months before it comes back.

I've got the same issue with my Outie and I've been doing the same thing, along with making sure the phone is removed from the bluetooth system. It happens in the car less frequently than with my headset but I guess I have grown use to it since my headset is also doing the same thing. Dealer didn't have a clue what was going on either and since I didn't want to reenter all my phonebook entries in my "replacement" system, I've elected not to have the module replaced.

 

I was also having issues where my 2009 would lose pairing and phone book. The dealer does not troubleshoot this, I had to spend about 45 minutes on the phone with the folks that provide the warranty for the system. They gave me a ticket number to have the dealer replace the system located behind the nav screen. I did insist that they update the system map at the same time to bring it up to the 2009 map since they sold me a new 2009 with a 2007 map. They gave me the disc and dongle, it took 2 hours, but it brought the system software up to revision "I" from "F" as well as updating the map. It has now been working fine for 4 months without an issue.