Car sound goes silent intermittently

Hi, I don't know if this is a bug but sometimes while free roaming or during races the car sound goes completely quiet.
You can still hear the air intake, blow off valve sounds, other cars, NOS, tyre screeching etc everything except the engine sound.
To get the sound back I have to go in and out of the garage or start a race, anything that takes me through the loading screen.
Anyone know if this is a glitch/bug or is anyone else experiencing this issue?