thank you for your kind replies, I think I should give more information about the measurement. 

The sample is a sealed battery anode consisting of silver particles that should undergo alloying with Lithium during charging. This is done at constant temperature and applied pressure. I repeated this experiment under different conditions several times, and each time there is less noise before a certain time during the charging process, after which is persists even when the battery is at rest (not charging/discharging). I0 also did not fluctuate much, and the integration time for each point is indeed the same. Therefore I think it is not instrumental, but rather something happening in the sample. As you can see from the spectra, the silver particles experience a strong decrease of uniform structure when they lithiate. For me, this at least explains why the noise in the post-edge increases, but can it also explain the noise in the edge and pre-edge?  

Best,

Sebastian