2011 F-150 XLT 4x4 5.0 170k miles. No auto 4x4; just 2WD, 4 high, and 4 low. I've had my truck for a long time, and during my ownership, I've never had any issues with the 4x4 system (other than the actuator motor that I changed). I use my truck during hunting season, that's about it. It's not a daily driver since I have a work vehicle, but I do keep up with the maintenance on it. A couple of weeks ago, I took a long drive pulling a 4-wheeler. At 70mph, I had this noise that sounded like a plastic trash bag caught underneath it, thrashing in the wind. I pulled over and couldn't see anything unusual. I continued the trip, and it got quieter. I did an oil change/tire rotation and checked the brake dust shields and anything else that could be making noise; everything seemed normal. Then I used it for a trip a yesterday at 75mph, and this awful noise came back (but louder.) Once I got to my destination, I drove around the town, and the noise would happen under under accelleration but would stop if I put it in neutral while driving. It seemed under load it was worse, with it getting quieter once the cruise was set and the rpms lower. It seemed like it was 100 percent coming from the front wheels or engine bay. Once I got home, I thought it might be the heat shield clamps on the exhaust pipe...nope. The OEM clamps were all there and tight. Now I figured it was the damn IWE system I've heard so much about. I wanted to diagnose the check valve and solenoid, hoping this would be my issue. I merely TOUCHED the vacuum line going to the solenoid, and it crumbled in my fingers. The solenoid was good; it clicked on and off as it should when the 4x4 was turned off and on. The check valve also seemed like it was functioning. But I wanted to diagnose further. I completely unplugged and removed the solenoid, removed the broken vacuum line section, and put vacuum caps on the box that makes the vacuum, as well as capped the fitting that was now hissing. I took it down the road and got to highway and interstate speeds, no noise whatsoever. So, I figure now my wheel ends are now engaging my CV shaft since they have no vacuum. I have not yet pulled a vacuum on the wheel ends to test them individually, but I plan on it. Minus labor, OEM wheel ends, the vacuum lines, solenoid, and check valve will run about 350-400 dollars. If I go to the Dorman vacuum delete route, I'm looking at 130 for both wheel ends. I'm hoping that my hubs and CV shafts are OK). I guess my question is, what really is the difference in having the current vacuum-capped situation vs. going to the Dorman vacuum delete wheel ends? It seems like either way, the CV shafts will engage the hubs and spin, but I can't see THAT much wear and tear coming from that since the diffs aren't engaged (in 2wd mode.) I will eventually fix it properly, with a full OEM setup or the Dorman vacuum deleted wheel ends. Opinions?