Understanding fluctuations in strongly coupled, finite-density systems poses a significant challenge. The AdS/CFT correspondence offers a robust framework for exploring these systems via their gravitational duals. In this talk, I will present recent advancements in constructing an open Effective Field Theory (EFT) for probes interacting with finite-density holographic systems. I will also explore the deep connection between Hawking fluctuations and quasinormal mode dissipation, as captured by fluctuation-dissipation relations (FDRs). Notably, we have derived non-linear FDRs at finite density—results that are challenging to obtain through other methods—providing new insights into the dynamics of strongly coupled systems.