Gotta be careful changing that. There is some underlying problem causing the in game letter A (which is mapped to Z on the keyboard by default) to play that sound. What you did is basically changed that button so it doesn't exist and now does exactly as the the space, c, and enter buttons do.
By default RMXP has these keys:
L - Q on keyboard
R - W on keyboard
X,Y,Z - A,S,D on keyboard
A,B,C - Z,X,C on keyboard.
The C button has a few different ways of being called such as enter and space. Keep in mind when developing, that YOUR changes to the keyboard will not effect OUR changes. If that sound played when you pressed 'Z' (A), then it will still play when anyone else presses 'Z' (A)
Hope i wasn't too confusing