Car Tech: Pioneer Nav Head Unit Problems...

Pioneer Nav Head Unit Problems...

I had a Pioneer AVIC-D3 navigation radio installed in my '07 Chevy Tahoe. They used the GMOS-LAN-01 "brain" unit, which allowed me to keep OnStar functioning, plus the wiring harness to keep my steering wheel controls functional.

OnStar and hands-free calling still work, however there's some glitch in the second it takes the system to mute the radio and initialize OnStar or hands-free.

In essence, when you push either of the buttons, the first split-second of audio is clipped. For OnStar, it's not a problem, because that begins with the musical notes. For hands-free though, it sounds horrible.

You get: "...tar ready!" or "...ar ready!"

Is this a known problem with no solution or did my installer get something wrong?
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A second question. They first put the nav antenna on my roof, running up through my windshield molding. I made them move it and now it's on my dashboard. The installer claims this antenna can't go underneath the piece of dash trim where the factory nav antenna would go (by the automagic headlights sensor). The install guide also claims the antenna needs to have a view of the sky. So is the factory nav antenna different somehow?

Any guidance greatly appreciated. Thanks.