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It's possible that the noise could be coming from the transmission but it could also be tires or wheelbearing noise.
Take a look at the tires and make sure they aren't cupped or chopped. Tires can make noise very similar to bad wheel bearings when they have uneven wear.
Take the car for a ride. While it's making the noise gently swerve a little to the left and right and see if the noise changes pitch or goes away when turning one direction or the other. If it does then you have a wheel bearing problem.
If tires and wheel bearings can be ruled out then the noise is most likely coming from the transmission, a stethoscope while running the car on a hoist or Chassis Ears can be used to make sure the noise is in the trans before replacing it.
It's definitely possible to have no other symptoms besides a noise. There are many components in the trans that can fail and make noise but not immediately cause a performance problem.
If it's making noise then unfortunately changing the fluid isn't going to help, so I wouldn't waste any money on that.