Aera 510 problems

I have a problem with my Aera 510 freezing intermittently usually but
not always on start up. I get to the initial Garmin logo and that's as
far as I get. The only way to fix it is to remove the battery for 8
hours or so and try again. It happens intermittently and I can't relate
it to anything. Occasionally, but less often, it will freeze in flight.
Plugging or unplugging the XM antenna doesn't seem to impact it. I've
already sent it back once to Garmin for a cost of 300 bucks to get a
replacement unit with the same problem. I've seen others complain about
this, but of course the drones at Garmin tech support claim to have
never heard of it before. I have the latest unit operating software (3.50)

Has anyone seen this behavior, and do you have a fix? Garmin's pretty
unhelpful on the problem.