No idea who it is.  We got an unexpected call from 301-549-5013, too.  The CNAM was set to "UNAVAILABLE" (Our carrier's logs don't display that string for incoming calls that have no CNAM info set.)  Our third-party blocking service seemed to intercept this call after one ring.

Called and left no message after I ignored the call
A week earlier I got a call from 301-232-3587 where the caller was also labled SANDY SPRING MD