i dropped my 06 4.4i off at the dealer for almost the same thing. my problem is a fluttering sounds when the fan/ac unit is on when you are at idle and when you press the gas peddle. sitting at the starbucks drive thru with the window down it's quite obvious. sorry, but i don't think that's normal, and you shouldn't hear the fan/ac unit in the car in my opinion. the "normal" operation was already said, but i also have had a strange sounds when accelerating hard, sounds like the mufflers are buffered. definitely doesn't sound like a normal v8. then i turn the fan/ac unit all the way off and all the sounds go away. i'll post tomorrow after the dealer tells me very thing is "normal"