2004 Chrysler Sebring Engine sound

I got an oil change and radiator flush today and when the mechanic was almost done with the flush he started the car before he replaced the radiator cap, and the coolant squirted everywhere, he shut the car off and replaced the cap and started the car back up but my car sounded way louder than normal. Now when I turn the ac off it gets louder, then when I turn the ac on it gets quieter and sounds more like the way my car sounded before I took it in. The loud sound that I am talking about is that it sounds as if the gas pedal is being pressed constantly even if the car is just parked and idle. What miight this be caused by?