Sometimes No Vehicle Audio

A number of times I have been killed in close quarters by a Tank, Mobile AA or other armored vehicle yet I heard no audio for those vehicles. I mostly play Engineer so I am attuned to the sound of Vehicles incoming or moving away from my position. I use a fairly new 7.1 surround sound headset with War Tapes V.A.L in game.

I have not verified with anyone else on this issue. I did search for a bug report on this forum, found nothing related. I have noticed this a lot more on Blackwell Fields as I enjoy that map & have been playing it exclusively.