Indeed, looks like the civilian Cheetah has a siren as an extra. However, two things to note:
SilentPatch does not fix model/asset issues, so this is out of scope.
I can imagine this being 100% intentional, a fake siren put there to "scare" people. The fact VCPD Cheetah has a siren always and this is an extra seems to further imply it was intentional.
Because of the combination of those two points, there's nothing for me to do here.
The simple Cheetah for some reason spawned with the siren from VCPD Cheetah..