Why would a BLDC motor be "noisy" in reverse
When I was running slot cars with brushed motors in the late 60s I played with advancing the timing, by rotating the brush assembly until the forward rotation was fastest at a given voltage. This of course made the motor asymmetrical with regard to forward and reverse operation.

Your noisy reverse operation may be from a very similar situation. The motor with sensors may be "factory tuned" to operate more efficiently in the nominal forward direction.

One might try playing with the timing in the reverse direction to try to compensate for the (possibly) asymmetrical motor timing and remove the reverse direction noise. Tuning timing for minimum noise may do the trick. Hope this helps!