MacOS – How to rm /Volumes/Free when it is really free

Short problem background

OS X version 10.10.5, running on an iMac with no problem (uptime = 101 days).
I had an USB key, named "Free" mounted on /Volumes/Free.
I wrote successfully a file on it, and verified it successfully with
Disk Utility.
Then I tried to eject it from the Finder. This operation fired the beach balloon but no message was written on /var/log/system.log.
After a while the Finder displayed me an error message telling me
my volume couldn't be ejected because in use.

Since I needed the USB slot to restart the copy operation on another
USB key, I ejected my USB key "Free".
And the Finder displayed me the usual error message because the volume
was unmounted incorrectly.

Problem seen actually

I have now a directory /Volumes/Free which stayed in place and which I can't easily remove.

••On_my_Mac••% ls -@del /Volumes/Free
d--x--x--x+ 2 root  admin  102 Jul 11 14:01 /Volumes/Free
 0: group:everyone inherited deny add_file,add_subdirectory,directory_inherit
••On_my_Mac••% 

Neither Spotlight nor any other daemon stayed with this directory opened:

••On_my_Mac••% /usr/bin/sudo lsof /Volumes/Free
••On_my_Mac••%

Nonetheless I get the following error upon trying to remove it:

••On_my_Mac••% /usr/bin/sudo rm -rf /Volumes/Free
rm: /Volumes/Free/.autodiskmounted: Permission denied
rm: /Volumes/Free: Permission denied
••On_my_Mac••%

If I further try to analyze this filesystem problem, I get:

••On_my_Mac••% /usr/bin/sudo chmod u+rw /Volumes/Free
••On_my_Mac••% /usr/bin/sudo ls -@ael /Volumes/Free
ls: fts_read: Permission denied
••On_my_Mac••% /usr/bin/sudo ls -@del /Volumes/Free/.autodiskmounted
-rw-r--r--  1 root  admin  0 Jul 11 14:01 /Volumes/Free/.autodiskmounted
••On_my_Mac••%

I didn't try a reboot because this is not a short term an option on the server involved.

Which daemon is responsible of this situation?

How may I further analyze this problem?