It's all about the Software

To make clear that the waterfall problem is not related to CPU/GPU load, I borrowed the NVIDIA 1050ti card from my son's computer. I also enabled NVIDIA CUDA.
I did the same test getting very low CPU/GPU values but unfortunately I keep getting the waterfall freezing while adjusting the contrast.
Setup information:
Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz 3.40GHz
RAM 8GB
WINDOWS 10 PRO 64

I am available for other tests
Videos attached

Hi, It looks like the faltering reactions are due to the (older) CPU. You can't do much about that i'm afraid.
The audio clitches however sounds like HF interference coming from your monitor.
Trie some ferrites arround your VGA cable and all cables on your RSP1. Also listen what happens when you disconnect your antenna.

r/Leon