White self noise

My recordings (made with version 1.1 units ) have quite a lot of white noise and would like to compare to those of others

(in the 0 - 48 kHz range). As far as I understand from other conversations, this is different than the discrete clicks produced by SD cards.

Has anyone made test recordings within a soundproof box with different AUDIOMOTH versions

and different recording parameters (I understand different Gain options must have a lot of impact

in white self noise)?

Is there a guide with advice for deployment (i.e., which Gain use under different circumstances)?

Finally, can anyone suggest filters (and software) for reducing noise in post-processing?

Thanks,

Agus