[CQ-Contest] funny interference on 15m?

[RT Clay]

Sunday morning during CQWW CW at 1335z some kind of wideband signal landed on top of me. It had a pulsating sound and covered 21.040-21.060....on the panadapter it looked like a white cloud (I have a screenshot). I thought it was a local problem until I noticed many stations inside it qsying. 10 minutes later it was gone. Did anyone else notice it? What was it? Between my two antennas to the NE and SE it was loudest from the NE.

Tor N4OGW