You have a few options here.
1. Work a draw into the drill with the timer. So you do Draw 1, reload 1. Will give you a killer draw too.
2. Gun on target, reload, gun back on target. No timer. Alternate pulling the trigger before the reload and after the reload to ensure you have the proper follow through. You'll get more reps in this way and can really focus on engraining the proper habits.
I wouldn't train loads reacting to the beep...you will never see that happen in a match.
The biggest time wasters in the reload are two things. The speed your hand gets to the new mag, and the speed the old mag is ejected. Focus on completing those tasks at the earliest possible instant.