Does cutting out the metal grill have a real effect on noise or air flow?
Depends on the grill, if the noise characteristic doesn't change when the fan is running in clear air then cutting out the grill will likely have little effect.
Its not normal for Nexus or any good fan to wear out in 9 months, i have Nexus fans that are over 5 years old and still totally silent so it does seem odd that yours is like this.
The only other thing i can think of is lubricating the bearing,
If you carefully peel the sticker of the back of the fan you should be able to remove the dust cap/plug, add a few drops of oil into the bearing spin it by hand a little to work the oil in then replace the cap/plug and sticker.