why are my airpod pros automatically switching to transparency mode

my airpod pros have recently started switching automatically to transparency mode, and i cannot turn it off. when i try to do so, i hear three quick beeps and the headphones return to transparency mode/ANC mode. why can’t i turn either mode off? i’ve tried resetting the airpods, forgetting the device, etc. which works for about 5 minutes, but then the transparency mode notification beeps and i can’t turn it off.