Rattling sound in elite series 2 controller

So my warranty is over on my controller. By a few months and I seem to have this issue with multiple elite controllers. That just over time something on the inside seems to start rattling. The controller is well kept. Cleaned regular. Never dropped. So why does this sound consistently keep happening out of the 4 elites I've owned (1 elite series 1, 1 elites series 2, 2 elite series 2 core) the series 1, 2 , and one of the core ones have done the rattling

:)