Gain and Noise

[LawrenceHill]

@Overtly5280

Any help/advice greatly appreciated.

It is quite normal.I think the answer is in this thread:

Strange noise level behaviour

Noise includes partial messages, at night you get fewer of those. In other words, noise is influenced by number of planes. The weakest signal is a much better measure of effective noise as it shows you how weak of a signal you can receive.