A friend of mine has a 2004 f-150. He is registered but it will not let him post a question. I will describe the problem as written down for me. I have a rattling sound when traveling down the road under power. It is not there when coasting or idling. It goes away in 4x4. Unplugged the vacuum module to the 4x4 switch and it goes away. Re-placed the module and the rattle is still there. It sounds like a spark knock or the damper rattle the old GMC,s use to have. Any help would be appreciated. Thanks. Brent.

 

check the check valve on the vacumme system for the 4x4 soilinod.sometimes the check valve gets debris in it and wont allow the system to hold the engaugment rings in the hubs in the unlocked posision.these systems work backward than your normal 4x4.it uses vacume to diengauge the hubs.older/other systems use vaccume to apply the hubs.