I'm sure this has been discussed before but I don't remember it.
In the original game there is no grenade reload sound associated with the AR. The grenades just appear in your inventory and there is no reloading animation. The AR bullet reload reuses the Magnum reload sound (as far as I can tell) and there is a reload animation.
In Aleph One beta, there is a grenade reload sound but it is the same as the Magnum reload.
Does anyone remember if there was ever a grenade reload sound in the Marathon sound file (just never used). Perhaps in the Demo?
Anyways, to make the AR in the beta the same as the original, the grenade reload sound will have to go.