i ran into this problem on my Canyon when i installed the roof rack and the lights on the rack. if the truck was facing one way (example North) i'd get crapy or no reception. if truck was facing (example) south, great reception. took a while of researching to figure out. finally, i tore into it and found out i was able to just stretch the oem cable out for it to reach to the top of the roof rack. the cord was long enough. i just wrapped it in electrical tape, then wire loom and more tape. then lots of RTV to seal it all up. now the XM works like the rack was never there.
NICK ~ CrazyEyeZ
2005 GMC Canyon Z71 4x4 crewcab < 355Nation.net >
-2" lift shackles, TB's cranked to level, Rancho shocks, 31x10.5x15 FireStone DestinationLE's
-roof rack, 24v LED flood and spot lights, 2x 4ft FireSticks, Cobra 29 classic w/weather
-custom HD bullbar with 4 130w KC DayLighters