Ideas for minimizing self noise?

We are getting ready to deploy audiomoths for a project in central California to record in the sonic range (sample rate 48 kHz) and have just start to test a few of the units and I have noticed a lot of self noise. Has anyone figured out how to minimize this noise? These units were deployed in Tupperware cases with a goretex cloth sicker over a 15/64" hole. they had the three internal batteries installed ( Duracell AA 1.5V, new, Alkaline). AudioMoth 1.0.0 with the 1.2.0 firmware. We have two models of SD card: SanDisk mobile Ultra 32gd microSD HC I and SanDisk 32gd microSD HC class 2. We put three devices out with gain set at 0, 2 and 4. all three recorded and biological sounds were audible and visible on the spectrograms but there was also a lot of self noise on each (slightly different types of which I have provided examples of two of the devices below). (updated)