The contactors are a part of the electronics in the heating system of the Jacuzzi. When the heating system is activated, the contactors are used to transfer voltage to the heating element. If the issue is with the contactors, in addition to the buzzing noise, the Jacuzzi should either not warm up or warm up much more slowly than normal. You should replace the contactors if they are making a buzzing sound.
The pump on a Jacuzzi can produce a variety of different noises when the bearings inside the motor start to wear down. The bearings inside the motor prevent the moving parts from touching one another when it is in use. If the bearings wear down, the parts start hitting each other, causing noises, such as buzzing, to be produced. If the pump is buzzing, you should discontinue use until you replace the bearings. You can damage the motor if you run it extensively with worn-down bearings.
A case of worn-down bearings is not the only pump-related reason a Jacuzzi might start buzzing. The capacitor inside the pump can start to buzz if it is faulty. It is possible to distinguish between the two issues by carefully listening to where the buzzing sound is coming from inside the pump. A buzzing sound coming from the electronics is the capacitor. You should replace the capacitor if it starts to buzz.
Bees sometimes build hives inside walls, under decks or in other enclosed areas. If the buzzing sound is coming from the Jacuzzi, but not from any of the mechanical or electronic parts, this may be an indication of a bee hive. You can usually also identify the presence of a hive by an increase in the amount of bee activity near the Jacuzzi. The hive will likely be located under the deck near the Jacuzzi rather than on the Jacuzzi itself.