2007 5sp, When the car is first started this does not happen but after it is warm it sound like one of two things either detonation or misfiring, It reminds me of a pot of boiling water on the stove with a lid on it letting out pressure by a lot and then a little back and forth -- car can be used all day long and is not over heating but as soon as I hit the AC button the rumbling starts, AC blows cold but I am afraid of leaving it on very long. I have NGK Laser plugs in it if that means anything. Someone at the parts store said it might be the belt is either to tight or to loose or the AC clutch is binding and I guess messing with the alternator output. Thanks for any info.

 

Take the belt off and spin pulleys by hand to duplicate a noise