Ford 2004 F150 XLT crew cab 5.4 L four-wheel-drive 98,000 miles. Problem. Started hearing this loud hum growling howling sound which appeared to be coming from the truck front end compartment, four-wheel-drive transfer case area several months ago. This noise happens about two times per month, then no noise for weeks. Occurs at lower speeds of 40 mph and lower. When I hear this noise I will slow down then stop. When I slow down and stop the noise stops. When I resume my driving after I stopped the noise does not reappear. When I come to a stop the noise goes away while the engine is still running. There is no noise when stopped at idle. The noise subsides. Happens only when driving not when idling. No high pitch noise. Possibly sounds like Gearing, four-wheel-drive transfer case, CV joint,? however steering is not affected able to turn left and right with no problems noise happens when driving straight or turning. No loss of power or hesitancy. AC and heater and lights are off when there’s noise happens

 

Transmission fluid level good. When I hear the noise again, I’ll put in neutral and see what happens? I jacked up the truck to check hub bearings. Feels fine. Don’t know if dealer has heard of such a random noise.