We have several cars in our base and there are 2-3 of them with broken windows. When I log in, in the first few moments it sounds like someone is actively shooting out the windows with a silenced weapon.

I have also observed there are several other sounds which exhibit the same behaviors:

Fence Gates Open/Closing, Magazine being partially re-loaded, etc. I do not have any information on these other two but I do notice them, and it's always consistent with when I log-in.