If you have just ID'd a threat, you should have that threat covered with your primary weapon. If you are going for your secondary weapon on your tactical vest in this situation you've much bigger problems than noisy velcro.
BTW-if you don't open your velcro in the mud, it won't cause you a problem.
However, if you must open it in the mud, pouring water over the loop pile to rinse the dirt off will restore its holding ability. (Been There, Done That.)
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May your lead always hit center mass and your brass always land in your range bag.
~Blades~