I agree on the overloading and probable cause, but there are a couple of other possibilities
!5000 khz. is close to the third harmonic of Radio Cristal on 5010. They have a notoriously drifting signal. However Cristal is tough to hear on it's fundamental frequency, so I doubt that it's them.
Now, if the Cubans are using 7500 khz. all bets are off as 15000 khz. is it's second harmonic. The Cubans are all over 49 and 41 meters these days.
BTW, try checking 5900 khz. if you hear it again. A portable with too much antenna is prone to images from 900 khz. above the frequency it's tuned to. You became the ground side of the antenna when you picked the radio up, which caused the overloading.