New to this site. I have a 2004 f-150 four wheel drive. Started to notice a roaring noise in front end. After jacking up the left front end and spinning the tire I hear a clicking noise. Replaced hub assembly same problem. However if I put it in four wheel drive and turn off, the clicking go"s away. When I shut the truck off a few seconds later after spinning the tire the clicking comes back. Even if you do this process while driving you still hear the roaring. Any help would be great.

 

Check the vacuum hoses to your 4wd actuators (auto hubs). One might be crimped or has a hole in it. The actuators work off of vacuum when you start the engine. If no vacuum is present then the hub will try to engage and you will get a nasty grinding sound. It's a single small hose. There is the brake hose, which is metal, the ABS hose which looks like 2 hoses fused together and the vacuum hose. Same thing happened to me. Good luck.