I have a 2014 Ford f150 5.0l 4wd. When I turn full lock or hit a bump I start heating a bad growl in the front end. I can pull over swap my truck to 4wd high and then back to 2wd and it goes away until I hit another bump. I have already replaced the vacuum lines, and had my vacuum pump tested as well as change the drives side wheel hub because it had grease running out. I was assuming the wheel hub leaking may have been causing a vacuum leak not the case. I have also checked both driver and passenger side 4wd locking hub seals and they seem to be in good condition. Anyone else had this issue, or anyone know how to correct it . Thanks in advance