Just wondering, if you had a weapon that did sonic element damage (ala fire, cold, etc) does it need to make noise when it smacks things (ala thunderstone/etc), does it need to be loud/noticeable?
A thunderstone, yes ("it creates a deafening bang" uese onomatopoeia, which implies that it's audible).
Other sonic effects: Well, let's look at the description of sonic:
Sonic: Sonic effects transmit energy to the target through frequent oscillations of pressure through the air, water, or ground. Sounds that are too high or too low for the humanoid ear to detect can still transmit enough energy to cause harm, which means that these effects can even affect deafened creatures. Sound effects can cause hit point damage, deafness, dizziness, nausea, pain, shortness of breath, and temporary blindness, and can detect creatures using batlike echolocation.
So, they do not have to make noise--at least, they do not have to make noise that a human can hear. Ultimately, the GM will have to arbitrate whether (and to whom) a sonic effect is audible.
So when added to a weapon, in a sense you can make a 'vibroblade'?