AM's quieter (I think)when conditions are quiet. Anytime you see one of our radio compatriots across the big pond talk on their sets while using FM they usually have their squelch turned up enough to cut the static noise out. The company I work for used to use a FM business radio/repeater system. The squelch was set by our resident radio tech/fix it guy.
However nowadays my company has switched to PTT cell phones with Trackit GPS capability in order for our dispatch to keep track of our fleet of mixer trucks.
actually fm is quieter [if squelch is properly used] nice mode to use when theres 9 sunits
of dx . just go to fm set the squelch and its nice and quiet