My truck was having some vibrations and was making a strange scraping noise coming from the front left tire. I had Les Schwab look at it and they said the vibration was coming from the HUBs and they didn't know what the noise was. Today I replaced the front hubs on both sides and the drivers side 4wd actuator because the gears were all messed up. Now it is making a similar noise just in a different way. Before I did anything it only made the noise whenever I was accelerating heavily (usually started about 30+mph) or when I was accelerating up hill in 2wd. If I shifted it into 4wd it would immediately stop. The noise was a long rattle/scrapping noise.

Now that I've changed out the actuator it seams to happen whenever I'm accelerating but instead of a long steady noise it happens in short bursts and sounds like small bursts of air almost like a vacuum leak of sorts. We pulled the vacuum line off the solenoid and did a vacuum check and it held vacuum fine. The noise actually sounds like the noise my buddies vacuum gauge made. Any Ideas?

05 F150 SuperCab XLT 5.4L 4X4

 

Almost sounds like a vacuum leak.

 

Replace the check valve. If that doesn't solve it, then replace the solenoid.

 

Where's the check valve?

 

You have an 05, so that would put the solenoid on the firewall on the passenger side. The check valve will be close to that. On the line going to the hubs. Also, you may want to put a water guard above the solenoid. They have been known to get water dumped on them in that position. Matter of fact, you may just want to replace it with the new one which will have the rain guard built in.