It must be the whole HD set up. I have xm through my garmin 665 with the GXM40 receiver magnetically attached to the radio chassis in the fairing. I sometime play through the aux port with stock speakers, sound ok but could be amplified. Generally I listen Bluetooth through my unclear head set. I rarely have loss of signal unless I have dense Forest on the south side or tall mountains close on the south side.
I mounted mine with wire going up between windshield and the flat part of the inner fairing. I have those add on tweeters so you can't see it and it's magnetic. I doesn't work inside of fairing!! Works great.
Its pretty close in my truck. Factory stereo and it kicks ***
Oh, don't get me wrong - I love it! In my truck, in my last car, in my OL's car. . . They all sound amazing. But, it's not quite CD quality. It doesn't have the same frequency range.
I have the Xm express model with The antenna is mounted in the fairing and I use auxiliary of the Harley head unit and I have the power hard wired to the bike. If there is lots of tree cover it goes out. But it's not bad. No different than in the car. I've heard people get better reception if you use the home antenna. They also have a motorcycle antenna but I'm not sure how well that works either.