On live server i noticed that bug very very often. Happens to all kind of ground vehicles.
I think it is related to the doppler effect of the engine sound.
You are spawned in and a vehicle comes towards you. As soon as it changes from incoming sound to outgoing sound (moving away) it goes muted. the only thing you will then hear is the track audio. depending on the distance to the vehicle it can be 100% silent from that moment on … at least for you.
Do you have a clip to share or is it happening to a specific unit more than others? I am wondering if its the engine idle bug #704
it is NOT the idle engine bug … i know that one
there is NO engine audio at all then
next question is if it only happens on my client or all clients around