The idea of something rectangular, same as the bed, was to let it move around fully to identify exactly the condition or motion when it makes the noise.
If it doesn’t do it when the extruder moves side to side then that rules out the X axis for the most part. Does it only do it when the extruder is near the front, near the back or closer to the middle. Only when it is on the left, or on the right. These are some of the questions to ask when you hear it. What is the position of things?
As far as cleaning just wipe the smooth rods with a lint free towel and add a few drops of a light oil and wipe onto the rods. The bearings are sealed anyway so just a little coat on the rods.