White-throated Sparrow would be be a surprise in MD, and they don't usually come in people's garages. My guess would be Carolina Wren.
If it is a Carolina Wren, that thing could be in full-blown territorial mode until August at least, maybe longer.
Distant second-guess, Song Sparrow. Prob'ly be done in a month.
I looked at pictures of the Carolina Wren also. Whatever it is, the SOB is skating on thin ice. The air rifle might be in use tonight.
