If it's a series cart the forward and reverse switch will be by your leg and the reverse buzzer is under the cover on the forward and reverse switch located under the seat on the passenger side of the cart.
If the cart is a PDS the forward and reverse switch is on the dash and the reverse buzzer will be behind the dash near the forward and reverse switch.
A piece of tape over the hole on the buzzer will quiet it down and it won't be so annoying anymore.