Rumble/Vibration at 65 MPH up

[spencermac11]

After a couple weeks of looking through every forum I could find on anything like this I still couldn't find an answer so I was hoping for some possible insight into my now seemingly extremely mysterious issue. I was driving on a highway Around 75-80 avg and went to pass someone at about 85 and heard what I thought was a thump or something break from the rear and then literally immediately after I felt a vibration like a rumble in the floor and seats. Since then I've been to 6 shops in total including 3 general mechanics, a dealer, a tranny shop, and a drivetrain shop. All tell me they have no concrete idea. No lights came on and I don't feel or hear a thing under 65. The work I ended up getting done so far is:

New front U-Joint and (balance supposedly)
Balance/Rotate Tires
All new wheel bearings
Already had a new rear drive shaft when I bought it
New front right CV joint
Alignment
Rear rotors and pads replaced with new e brake shoes (they were gone completely)

I'm having the rear u joint replaced tmrw along with replacing the rear pinion seal and differential service. I have a 2004 explorer 4x4 with the 3.73 LSD.. I've scowered through countless forums to no avail. Just hoping to find some help. It only does this at that speed range and has no other issues or symptoms other than that.

 

[Meat_PoPsiclez]

If it's a 4 door I'd check on the 5th shock (top of diff case to frame). That's the right range for vibration when that shock is removed or ruined (or omitted as in the 2dr's). That shock is only there to damp vibration starting at around 60mph, and eventually smooths out above the range.

Otherwise, check the shocks in general?

 

[spencermac11]

Okay thank you, does my 4 door 2004 have this 5th shock even with the independent suspension?

 

[spencermac11]

Anyone else?

 

[BarryCarey]

Have you checked to see if it threw a wheel weight on a rear tire? Could explain the thump if it hit the wheel well.

I had a shaking issue over 70mph that I couldn't track down. I replaced far too much crap trying to fix it.

It turned out I had 1 tire way out of balance. Had them balanced and it fixed it.

I initially dismissed it being balance related since the tires we were brand new when I got it. Would have been far cheaper to have them checked as a first step instead of last.