This is definitely not a radiator fan. Only happens when they are backing up/low speed. I believe it is a user configurable thing. Whether it defaults to making noise or not, I have no idea.It might be user-configured on Teslas sold before March 1st 2021, but since then it seems to be mandatory, or at least have the default factory setting as "on".
Some rad fans sound very much like a quad copter drone.