Thanks Carltm for the advice.
But this solution only work till the current session ends.After that it creates the same problem.
Anyways I announce that I got the solution of the problem myself,that was just a sily typo

...In ..../rc.local file I accidently put /sbin/rmmod/pcspkr , that's why the changes were not getting reflected. I corrected it removed the unwanted "/" . Now everything's fine.
Happy Linux.