Help!!

engine makes a (rather faint) tapping noise when I try to accelerate. I am kind of confused, because it is good during idling(so it can't be the engine!) and it is also good when I'm driving but not pressing on the gas pedal(so it can't be transmission/tires!)

noise is present only when I try to accelerate, around 40 MPH.

its a Mazda Protege 2001, manual transmission.

Sounds like its pinging to me usually associated with poor fuel quality or engine timing too advanced. Try getting through a tank or two of premium fuel. There is not much you can do about your timing as the computer will take care of that. Good fuel should solve this if it is only fuel. Pinging can get worse as engines get a few klms up too

Sounds like a wrist pin/piston.