So that's what I may have been hearing on WTOP, 1500 in Washington DC.  It's
sort of a rushing noise, a bit like older TV sets used to put out on the AM
bands.  If that is the source, I have never heard WTOP advertise that they
are broadcasting digital and there wouldn't seem to be an advantage since
they ar 24 hours news unless AM stabelizes reception for a given distance.

Is there a listing of U.S. stations broadcasting digital?

73
Bob Martin
KC3FI

PS Hope this letter doesn't bounce due to format.  Changed mail program and
settings.