if the nscoutsahp and nscoutsahp2 don't have sounds, that means you don't have Jacobmaate's SAHP pack.

There are two solutions to this :
1- Download Jacobmaate's SAHP Pack
https://www.gta5-mods.com/vehicles/sahp

2- Go to :
mods > update > x64 > dlcpacks > nscoutpack > dlc.rpf > data 
Open vehicles.meta in Edit Mode and replace the audionamehash for the "nscoutsahp" and "nscoutsahp2" to "nscout"