This is my first post.

Re: 1998 F150 4.6L moderate clicking, crackling, slapping noise in the front passenger side engine compartment. I took off the serpentine belt and the noise went away. Put the belt back on and I removed the clutch and still heard the click. I detect no noise from the AC spindle. With the belt on using a stethescope I could detect the click on the idler bolt and the tensioner arm. I replaced both pulleys.

Using the stethescope the greatest sound comes from the AC muffler. When you turn on the AC the sound becomes 3 times more pronounced. Any ideas?

 

Sounds like the A/C compressor is on it's way out.

 

When I put the stethescope on various parts of the compressor there is no noise. When I have the clutch off I can put the stethescope on the spindle (which does not move) and there is no noise, even though there is noise up on the muffler.