I would prefer to script the vehicles into the mod as it would be neater
---------UPDATE-----------
I fixed it by adding
if (StrCompare(v.GetPrototypeFileName(), CAR_98) == 0)
soundID = Audio::PlaySample3D("mod:Audio/FX/Sirens/PH7009.wav", CarPos, true);
and that seemed to work. Thanks for everyone's input!