You may need to add a Filter between Antenna and the ProStick, even though ProStick Plus has a builtin filter.
Most likely some powerful Cell phone or other communication transmitter was installed in your area which is causing this problem. It is not shown in your scan because its frequency may be outside the range of scan you have done.
Better try this scan. It covers full frequency range of Dongle, and is pretty fast.
Spektrum - How-to Speedily Scan RF Noise in band 24MHz ~ 1800MHz
The results of scans are below:
The scan 1 shows RF noise picked by antenna and processed without any filter , The scans 2 & 3 were done with filters, and show how filters remove this noise.
Scan 1 of 3 - FA Antenna + Generic DVB-T (no internal or external filter)
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Scan 2 of 3 - FA Antenna + ProStick Plus (Only Internal filter of ProStick Plus. No External filter)
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Scan 3 of 3 - FA Antenna + ProStick Plus (with internal filter) + External Filter (FA Light Blue)
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