So Topless hasn't added this to the dang Gifu yet so I did it myself well, ajanhallinta did after my failed coding attempt. Have fun (i'm not going to tweak the sound distance much more really sorry i did my best).
How to use the mod: Put Gifu in reverse. That's it. the sound will play when ever Gifu is running and in reverse (so put her in neutral when you're doing jobs).
If anybody knows a better sound for the mod please, suggest it to me and i might change it!
Install: drop the contents of the zip into your MSC mods folder.
Video of Game Hard 4.0 using my mod. Thank you game hard!
TODO: Add it to where handbrake also cuts backup beep sound, this is subjected to change however.
Credits: ajanhallinta for basically writing a whole new file after i went to him with my failed code, Me for the idea and writing the origional code idea, Topless you glorious bastard for the game.