glasspack dual exhaust chevy 350 vortec?

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Hey guys i have a 98 gmc sierra 5.7l vortec with manifold back true dual no cats 2.25 piping with 2 10'' sweet talker glasspacks 3.5'' tips any ways when i start up my truck when its cold both my exhaust sound smooth crisp rumble anyways when my truck warms up my passenger side tailpipe starts sounding different it sound like a muffled kind of sound and the drivers side tail pipe sounds the same the whole time anyone help me out? Also this is when my truck is in park idiling