bwhite,
Where are you monitoring from? On my way to Towson last night from York, I noticed the same thing you describe, until I crested the hill just north of Shawan Road. After that, it sounded find. I didn't think anything of it until I was headed back up north. The signal stayed fine again until I crested the same hill. This lead me to believe that there is an issue with the Spookhill lowband transmitter; it's either out of sync with the other three transmitters or transmitting dead air. I had a friend of mine notify a guy at BCo electronic services, so hopefully they're on it. I hoped they'd have dealt with it right away, since, from the way the tones sound to me (distorted and broken) I doubt they'd consistently activate pagers correctly.
If you're monitoring from somewhere in the north County, I'll bet you're getting the same thing.
PS- Lowband is only transmitted from Towson, Spookhill, Catonsville, and Northpoint, so if the Spookhill site goes down, that leaves quite a dark footprint for lowband in the north end, which is extra-fantastic since coverage up north is 99.9% volunteer!