From my understanding of what he was looking at in regards to sound activated traps, disarming would be accomplished by setting the device off from a safe distance with, say, a rock, or unplugging the power source. The thing with the rule for triggers is that it specifies that the trigger must be visible, but doesn't specify the same in regards to the triggering mechanism or portion of the trap that activates it, so you can hide a fishing line tripwire or bury a pressure plate. Unless either my wording or the wording of the rulebook is in error.
Either way, the only tool required to reset the device would be one, maybe two hands which every marshal I've encountered keeps... wait for it... handy.
Wakka wakka!
EDIT: rather, the wording specifies both using the same term, which makes very little sense. Unless I'm mistaken, the trigger of a standard trap is what activates the sound/light/effect. Meaning that the rulebook is either saying that your tripwires or pressure plates need to be blatantly visible (which kind of reduces the usefulness of traps) or that the portion of the trap that produces the effect when triggered is visible (which also reduces the usefulness of traps, but at least makes it a challenge to identify the trigger and disarm it).
EDIT the Second: After browsing every instance of "trap" in the rulebook, it seems pretty obvious that the latter interpretation is correct, as there are several examples of traps listed in the book that have concealed triggers, where trigger means the part of the trap that the player interacts with to cause the trap to go off. Long story short, the wording for traps in the book is misleading. That being said, so long as the actual sound-making portion of the sound-activated trap is visible and accessible, it fits all the rules for traps. I think this merits a Marshal verdict and probably ultimately one on a national level.