Unexpected (unknown) behaviour ..

Hello all,

OS: XPsp3

A short while ago I noticed that my 'puters loudspeakers where muted (the 
systray loudspeaker icon showed a small round red "X" sub-icon), while I was 
pretty sure I did not do that myself.

Some days of monitoring thet icon revealed something rather unexpected : 
regardles of having FF, explorer, word or notepad open, typing ctrl-F + "1" 
* caused the "mute" setting to toggle.

(Tryping ctrl-F + "2"..."9" doesn't seem to do anything, I checked. :-) )

* causing FF to pop-up it text-search bar and Explorer to open its search 
sidebar. Word and notepad open their "search" dialogs. The "1" keystoke 
doesn't show.

Question:

Does anyone know where that that behaviour can be configured ?

Regards,
Eudy Wieser