files which change during normal execution

["Mehta, Rohit" <rohitm@engr.uconn.edu>]

Hi I am configuring tripwire for one of our Debian servers, and am puzzled by some files
which change modification time during reboot.

Included are:
/lib/modules/2.2.20-idepci/modules.dep
/lib/modules/2.2.20-idepci/modules.generic_string
...some other modules...
/lib/modules/2.2.20-idepci/modules.usbmap

The data (md5 checksum), filesize, inode, etc have all remained static, but the modification
time has changed on the reboot.  I did not update any modules, so I am wondering what the
issue is here.  I certainly would like to know if someone replaces my modules with evil backdoor
modules.

Should I be concerned about the updating modification times?  

Thanks, 

Rohit