[root@bear-05 ~]# for I in `seq 1 10`; do mount -o noatime /dev/sdb12
/mnt/test; time find /mnt/test > /dev/null; umount /dev/sdb12; done

Hmm. If you do the find so quickly after the mount, isn't it possible that the kernel is still reading in some metadata structures asynchronously, or checking the journal, etc?