Homer, as you're aware the Vector/Sigma is much more sensitive in the base of the antenna due to the radials affecting the antenna more-so that the conventional 5/8 wave. Let us know which Vector you tried to emulate. I'm sure you posted it somewhere in this thread, but that would help.
Do you recall the complaints I got from two customers some years ago that that I often talk about, and maybe even in this thread. They bought 31' foot CTE Saliut models from me. They each made their antennas as long as they could and tuned them. They complained that they talked alright, had a good match, but the receive was no good. Is that more or less what you are seeing, albeit you complaint is the white noise? They didn't specify specifically, but their problems could have been just as you described, if I read your report correctly.
BTW, that symptom can also be a clue that your common mode currents are out of control, increasing noise. I think you use a coaxial choke, but sometimes they don't work as expected, and I contend this is can happen if the choke is too long.
Since you have to take it down to adjust the gamma, check that out and let me know, so I can put the information in my bundle of good or bad stories.
Good luck,
