Is it still there, and how short was the pulse? Could this have been 13875 kHz instead? I mean, was 13874 kHz the tuned freq in USB or something like that?
If it was 13875 kHz, if the pulse was very short, around one eighth of a second, then you might have heard the Pips network, reported here:
http://www.hfunderground.com/board/index.php/topic,15272.0.html13875 kHz is a frequency they use often and the pulse repetition interval is 6.0 seconds for Pips. If you hear what you heard again, try some of the other frequencies on the list, it hits all of them in a given 6 second period.
T!