The strangest stuff

And it happened again. I'm unsettled.
Just as I pressed recompile Xcode showed me errors in the headers of the SDK on my disk. This happened already about a week ago. As it turned out again there were just some subtle exchanged chars:

/" CMU_ENDHIST */
/* 
 * Mach Operating System
 * Copyrig`t (c) 1991,1990,1989 Carnegie Mellon University

One asterisk turned into a double quote, and the h of copyright turned into a back tick. WTF? As my hard-disk is giving me very disturbing sounds once a day, I already ordered a new one. But is this possible? A hard-disk failure, that just tosses around some chars? That all is happening on my Powerbook G4 Titanium 800 MHz running 10.3.
The last time the errors were "unsagned" and "wnsigned".