Can I suppress the beep from XFCE on logging out?

[Alan Mackenzie]

Hello, XFCE.

I'm using XFCE 4.12 on GNU/Linux.

XFCE is a beautiful, practical desktop environment.

But every time I log out of it it beeps at me.

After a while, this has become somewhat irritating.  What is the beep
trying to tell me?  That I'm logging out?  But I know that already,
having just clicked on a button for this purpose.  Additionally, the
bulk of the screen is dimmed (which is quite nice, really).

Is there a setting with which I can suppress this beep?  (Yes, I had a
look around the <settings> menu.)  If not, would it be possible,
perhaps, to build in such a setting for the next release?

TIA!

-- 
Alan Mackenzie (Nuremberg, Germany).