I’ve have never used grease on belt edge just a thin layer of wax or silicone rubber lubricant on other 3D printer belt edge.
You can hear the sound even when the printer is turned off and moved by hand ?
Try placing a piece of hose to your ear to help locate the loudest point and narrow down the source of the noise.
Note:
This is the Bambu post I mentioned to you earlier.
SupportAssistantBambu Lab Employee
The squeaking sound can be caused by the belt touching the inside flanges of the idler
A solution to this problem is to add a very small amount of grease on the top and bottom sides of the belt, or on the side flanges of the idlers.
This will eliminate any squeaking noise.
But make sure not to add grease on the teeth of the belt, as it can generate belt skips.