Onstar problems

I am having problems with Onstar on my 07 Aura. On several occassions, it won't connect. It recognizes my "nametag" and the number shows up on my radio correctly, but I get "dead air" for about 20-30sec before the radio comes back on. I have contacted Onstar about this three different times. They have put me through to a service tech who runs some diagnostics and adjusts my settings. It will improve for a while, but within a few weeks, it's back to giving me problems.

Anyone have any ideas about this?