Popeye

I have a really old Hydrospa hot tub must be 25 years old at least and shes still going strong. Only issue i have is when you press the button to start the jets and open the two air valves either side of the start button you get quite a loud gurgling sound. Remember this is an old girl so no fancy blowers or ozone stuff just a quartes inch air line that goes from the start button at tub level and down to a little box between the heater and the pump. any ideas how i could at least reduce the gurgling noise. Thanks