I have listened to my moms ride a 97 altima and its real quiet compared to my 99si . My Si is loud as hell and I hear this noise and it sound like its coming from my belt and Im unable to locate it . How could I tell if its knocking.

 

screwdriver method? mechanic's stethoscope? What kind of knocking is this?

 

A grinding noise would be a water pump, mine went and luckily didnt take the timing belt out with it.

A clacking or tapping noise may be the timing belt, inspect and/or replace it immediately, Honda engines are of the type that bend valves when the belt goes.