I have the same problem. I live in Phoenix and I have an 07 Camry with dealer installed Sirius. I had Sirius on other cars with exterior roof magnetic mount antennas and had no dropouts.

But with the Sigma antenna installed on the inside of the window to the right of the rear view mirror, I think its getting poor signal strength. I hope there is somthing we can do. I'm going to take the Camry back to the dealer and have the tech look at it. I hope they have seen this before and know of a way to improvise an fix.

I'm sure its too much to hope that Toyota knows this is a problem and has a plan to fix it.

If this NO SIGNAL keeps up, I'm liable to get mad and rip the antenna off the window and stick it out the window. ARGH.