2006 Mazda 6 Making a clicking sound when accelerating

It started about a week ago i barely noticed it... but now i notice it all the time. What it is is after ive been driving around for a bit and for instance stop at a stop sign, when i start accelerating i hear this clicking sound, it only starts when i accelerate and it doesn't matter if i put it in park or neutral. I've had someone rev it while i listened all around the car for any clicking sounds both the all around the engine and under the car... its too faint to really hear it once i get going past about 30mph and i dont know if its just getting droned out or if it stops.