So I'm sure this has been covered a few times but I'm having some problems and if anyone can help that would be awesome!!!!!

So I have a 2003 Ford F150 SuperCrew 5.4L and 220,000 Km (136702 Miles)

Problem:

About a month ago I went to engage my 4x4 on the dash and all of a sudden I hear this loud sound (hard to describe) but you could here it and almost feel it in the truck. When I turned the dial back to 2wd it stopped immediately and you could almost feel the truck ease up.

So I put it in the shop at work and it seemed to let off.... So a couple days later I had to go through some big snow drifts to get to work, I engaged it and It didn't make a noise but every time I accelerated id get this vibration when I left off the throttle the vibration went away. So I went online and people were saying those solenoids. I thought perfect problem solved!! get it back outside click it into 4x4 and as I drive up a bridge I can here this tinging sound.... and this morning.... click it into 4x4 I again got this loud noise again.... gawd!!!

So another thing that may be helpful since I've owned the truck when 4x4 is engaged there is this hummmmmmm...... and if you stepped on it with snow the truck would hop.... now I can still here an intermittent hummm and id doesn't hop.... weird? solutions? A mechanic friend told me the hub? I don't know how to check these things or where to look..... help!!!!!! Ive changed the front diff oil in hopes that that would have helped with the hum didn't work.......

 

when you engage 4 x 4, two things happen. Electric motor on the transfer case engages the front axle, and a vacuum cylinder on the front axle pumpkin engages the driveshaft to the axle shafts. THe wheel hubs are engaged all the time and the front axle half shafts turn all the time. The disconnect is at the pumpkin. Easy thing to do is get under the truck and spray the cylinder rod and link at the front axle pumkin. Engage the dash **** and watch the cylinder go in and out. Tap with a hammer if it needs assistance to full stroke. Other than that, there is a fork inside to engage the axle, and the other end ... the electric motor... on the transfer case to engage and pick LO or HI.

 

As mentioned there is a shift fork. My brother had an 03 F150 SC that the shift fork had broke when he engaged 4wd one day. Not saying that's your problem but is possible.