I personally have been very disappointed with my Garmin 660. I had the "factory set up" with my 2010 RT-S Premier Edition. After about a year, I had the "sound problems" expressed in the first quote above. Garmin suggested doing a "soft boot" which meant opening the battery door, pulling the battery and then replacing, etc.
This worked sometimes and other times not. I too am suspect that it is the contacts in the cradle, but can't say for certain. I have no idea whether it's due to the weather or not.
I now have a 2013 RT-S and am using the Garmin 660 that I had on my old spyder. I'm still having the same issues, and the cradle is a different one. It's the cradle that you would have for a car with the suction cup. I don't have the factory set up like I did on my first spyder.
I'm just very disappointed that for the money spent, it has exhibited this flaw. Admittedly I haven't talked to Garmin about a fix. However, in another thread I saw that taking that course of action may only get you finger pointing from Garmin to BRP and BRP back to Garmin.
I may just scrap my 660 and get something else as suggested above.
Chris