I noticed that almost all RTL dongles I have tested do emit a heavy amount of RFI/Noise on the lower HF frequencies. If you look at the waterfall picture you can clearly see just how much noise the RTL generates. The RTL is plugged in but not being used. This is not noise going into the dongle itself but noise going out into my other SDRS just from being plugged in. The best thing to do is just leave them unplugged when not in use.