SDR spectrum anomalies
Periodic noise in an SDR spectrum is a common problem.  One likely source is EMI or RFI from nearby electronics.  

The sources of EMI and RFI can be from computers, USB cables, networks cables and routers, power cords, wall plug or internal power supplies for various electronic devices, wireless chargers, LED lighting controls and voltage converters, and solar panels, etc., even radiated from neighboring buildings.  This noise might rise and fall as people or controllers in other locations turn on/off lights and other devices. The power and high edge rates generated by some of these electronic components can radiate a vast range of periodic harmonics into the RF spectrum.

Kill the circuit breaker to your house or building, or wait for a neighborhood wide power outage, and a vast amount of this periodic noise in the spectrum might disappear.  Or, if you are lucky, you can turn off or unplug things nearby, one at a time, and discover the dominant culprit.  If you are running the SDR from a laptop and have a portable antenna, try running the SDR well away from any buildings and utility lines (for instance: a nearby park or open field, etc.)