Could be so many things.

Could be a broken belt on 1 tire.

Could be a small separation in 1 tire.
Usually from an impact or defective tire or improper tire repair.
A separation or broken belt will also usually show up as a wobble in the trueness pattern.

Could still be a wheel weight that flew off again.

Could be the balancing equiptment .. Not calibrated correctly or improper knowledge of useage or care taken in useage and weight installation.

You could roughly check your wheel and tires roundness/runout by running the vehicle until tires are fully warm. Pull into your shop and immediatly jack up the front first.
Hand spin the tire wheel assembly and look for radial and lateral run out to the best of your ability. You can use a tool up against the tread, sidewall, and wheel as well as Eyeball it while it is spinning.
Wheel run out data is an indicator but the whole assembly is what you are running on.

Make sure you start out with proper inflation cold on all 4 tires.
If you find a spot Mark it. so your mechanic or tire shop can check it out further.
OR......

Take it to a Known Quality Tire Shop and have them do it.

If that dosen't show any problems then you can move on to the rest of the possibles.

P.S. Do you have steel or machined aluminum wheels??
A bad steel wheel is a possible.
If you haven't owned the car since New then there could be damage from prior owner that you no nothing about.

 

My 2008 Panel is smooth as butter, my wife's 2010 has had a bad vibration since we brought it home. Just changed the left rear rim today, seemed to help but still has some vibrations at slower speeds. Have had the tires balanced twice. It's the original factory tires, going to try some new tires next. For some reason, it is just not as comfortable of a ride as the 2008.

Tman
Greensboro, NC

 

16" aluminum wheels, 1 replaced when my wife curbed it, bought it from a meticulous family member that told me everything that happened(which was nothing)...have all service records as well.

 

Since you think the problem has now moved, I would first re-check the rears again to make sure you didn't throw another weight and that they check out OK.
I don't 100% trust many tire dealers for precision balancing. Either they have crappy equiptment or they do not calibrate it properly or the operator is unknowledgeable or careless.
Seems like a lot of hassle but you really need to isolate if the problem stems from the wheel/tire asembly or NOT.
If it feels like it is now on the rear then they either moved the culprit to the rear in working on it, or you threw another weight.

With the aluminum wheels you have there should not be a problem unless one has been damaged somehow.

Personally ... I think I would work with the area that you think the problem is.
I would opt for 2 new know quality tires ( Michelin etc.) and have the tire dealer check the lateral and radial run out of the wheels when the old tires are off to eliminate any problem/question with these 2 new units.
Rebalance the new tires/wheels and put them on the front.
Test.
If no front end shaking but still in the rear then either do the same to the rear or move the fronts to the rear and re-test to see if the shake moves too.
If shaking moves too, then I would take the 2 used tires I just removed and use them to replace the shaking ones, or just do the same to the rear as you did to the fronts with new tires..
You can spend your money on Labor for Mechanics to do testing etc. with possibly no improvement, OR ... on replacing suspect items.
At least you would end up with some new tires instead of just mechanic verbal jargan.
I would try to make a deal for trading your old tires in, or put them on Craigs list to sell them.

 

When you have a vehicle that runs SMOOTH, do you really appreciate how lucky you are ?????

So many little things can totally Screw That Up.

 

Another thing to consider, but its really in the "one in a million" category, is a warped rear brake drum. Very rarely you can have a drum warp and every time it rotates it catches the shoes briefly and causes a judder/vibration. Its easy to check by just rotating the rear wheels with the vehicle on a lift to see if one "catches" during its rotation.

 

That theory and many others are valid in some cases, but in this case the vibration supposedly moved and the brake drum didn't.

Years ago when I was in the tire business, we used a Hunter Spinner to spin the complete front tire/wheel assembly on the car. That didn't fix anything but it did identify where the problems were and in that case it spun the brake drums too. Before the disk brake era.
Nobody worried much about the rears in those days. I.E. 3 way Front end Alignmnets. Now we do All Wheel Alignments.

A disc brake can cause symptoms as well.
I doubt anybody still has a Hunter spinner, but if you could find a dealer that could spin the complete rear assembly on the vehicle you might have a quick diagnosis. The thing is you have to get up to the speed of the problem.

 

843...that is definitely an idea that I had. The drums do hum a bit when decelerating from highway speeds or panic stops. I was looking at replacing them this fall. To the best of my knowledge, they've never been touched. I think the little clips are still on the stud, come to think of it.

 

I had the same problem with vibration with my '09 Panel. Took it back to the dealer several times. They re-spun and balanced all the wheals , the next time they put on 4 new tires . I had asked them in the beginning to check the shocks , struts , springs. They claimed there were no problems there. They finally told me that they ALL have a little vibration, I'm nuts, and to live with it !!
Well a friend of mine happened to be following me down the express-way, when we got to our destination he told me that my right rear tire was bouncing up and down like a freaking basket ball !!!!
I returned to the shop and told them about what we found and they immediately replaced the rear shocks....You guessed it , NO MORE VIBRATION ,and I'm NOT NUTS !!!!!!!! Hope this is of some help to somebody out there , nuts or not .........

 

I replaced the stockers with KYB's last spring...wouldn't hurt to check again I suppose. Definitely considering the drum theory. I lightly applied pressure to the pedal this morning and they are making more noise now than they were before, plus it's about time to do them anyway. Hoping that is the cause.