A most intereting problem. When I was reading the post, I was also wondering about some sort of metal coating. In general, a gas like this does not stop a XM signal.

Just another unexpected surprise!!!!
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The Rat. M80s, VP-150, QS8s, SVS PC 20-39+, OPPO, Onkyo 703s, Harmony 880 Sony 60" SXRD HDTV