This is something I have noticed for many months, since I started recording overnight on the SDR. I think the waterfall shows it best:
Time runs down, ie: it starts at the top of the image, at about 0858z, and stops about 2/3 of the way down, at 0905z.
This signal appears roughly around this time (0900z is presently 5 AM local time), I'll need to more carefully observe when I notice it, to see if it is really following any kind of a schedule. It sure looks like a switch mode PSU of some kind. It's only on for a few minutes, and I don't seem to notice it at other times of the day. Any ideas?