Ok this isn’t me, but when this guy says “reverse” at the 6 second mark it sounds almost exactly like that.https://www.youtube.com/watch?v=vfHN4DqF7Gw 1996 Saturn SL2 The rest of the video isn’t relevant. No Issues aside from that sound. usually happens when the car is just started
Check your ATF for a nice red color, if not, drain and refill and replace the filter. The filter is a spin-on cartridge just like your oil filter. If the noise continues, do a “reverse slam” procedure which is simply setting the parking brake and let it run in reverse for about a half hour.
The ports in the valve body that are used when in reverse can gum up since reverse isn’t used all that much compared to forward. After about a half hour, the new ATF should clean out those ports.
If the ATF is a really dark brown or black, drain and refill three times a week apart. Replace the filter on the first drain and fill at least, you probably should change it again on the last one too.