yeah just look for cracks in it
orrrrrr an easier way is to take your multimeter on continuity, put and test resistance between the the speakers and there points on the mobo, check my PulseVU tutorial for where the speaker mobo points are, there nice and big, thats the positives (red wires) ie left speaker red wire to left point etc, then pick either of the black wires (they are connected so it doesn't matter) and test there continuity to teh ground (i think)
that is all