Tapping sound

2002 mustang GT
I was driving home from work and a tapping noice started to come from the top end of the motor. It doesn't make a noice at idle just at throttle even in neutral. It will still tap while not being under any load. I am thinking it is a flat spot in the cam or a valve spring. Any idea what might cause this.
 
2002 mustang GT
I was driving home from work and a tapping noice started to come from the top end of the motor. It doesn't make a noice at idle just at throttle even in neutral. It will still tap while not being under any load. I am thinking it is a flat spot in the cam or a valve spring. Any idea what might cause this.
Hi, Think I replied to this before but you were in the wrong category....?