I have a 93 F-150 4x4 5.8 E4od. At around 55 it sounds like a leaf or water hitting a somthing behind headlight switch, kind of clickky. Is it a speedometer related? Its hard to describe.

 

no speedo cable on a 93.

 

You have a vent there. Does it happen more when running the fan on the vent setting?

On your year, I believe that your spedo is electric so no cable. I could be wrong though. I am sure others with more knowledge will chime in. I can only go off of my experience, which is limited on Ford trucks as I was always a Mopar man until I saw the light.

 

Its not fan related. It only does above 55 mph. Its not rpm related either, just speed. ??? Its not a daily driver, will check again this weekend.

 

You may still want to check the vent as more air will flow through it the faster you go. The fan may not push enough air to notice it.

Another thing to check is the firewall. You may have a hole (like most of our trucks do) that is blowing on some insulation or loose tape. You would only hear this at higher speeds. Just a thought.

 

These problems are always fun ones! Irritating and very hard to describe! Might not hurt to pull your dash and take a look! Or like animalistic said check for loose insulation or tape. Also might want to check your windshild and wiper cowl I had a noise that I could have sworn was coming from the inside dash but it ended up being the wiper cowl was loose.

 

My winshield trim did that at about 65 and up. Drove me nuts..took forever to figure out. put some urethane under it, quiet as can be.

 

I would check the firewall too. I had a hole unplugged down there for a stereo wire, and when I took the wire out I didnt plug it, and I heard a smiliar sound there. Plugged it up and its good to go now.