I have two cars with Sirius/XM - a 2010 Honda Odyssey and a 2012 Ford Focus. When sitting in the driveway, cars next to each other, same channel on both, the Focus sounds thin and garbled comared to the Odyssey.
This makes me suspect the quality of the receiver in the vehicles are the determining factor. I've heard talk shows where I couldn't understand what was being said (in the Focus).
Another tidbit...the Focus drops signals MUCH more than the Odyssey. When I go under the freeway overpass near home, the Odyssey doesn't miss a beat, but the Focus drops every time.
However, the Focus buffers up to 12 songs for replay...except the feature is a pain to get to...
Is it possible that one car has Sirius and the other XM? I know my XM radio suffers from dropouts a lot more than the Sirius radio in the same car. XM comes from three geosynchronous satellites while Sirius has three satellites that are not in a true geosynchronous orbit.