X3 Vibration...any advice?

[srhorn]

Well my 2004 X3 started a low speed vibration under load...I'd feel it shake at 20 mph, then again at 35-40 under light load. Brought it in to the dealer...he insistes it is the [COLOR=blue !important][COLOR=blue !important]Transfer [COLOR=blue !important]Case[/COLOR][/COLOR][/COLOR]. Not having the time to pursue it further (and I NEEDED the [COLOR=blue !important][COLOR=blue !important]car[/COLOR][/COLOR]) I said go ahead and replace it. Oops, didn't resolve the problem. To their credit they admitted to having egg on their face...and proceeded to try all kinds of ways to figure out the cause. They replaced lube in both front and read diffs, ran it without the front driveshaft, tried new [COLOR=blue !important][COLOR=blue !important]front [COLOR=blue !important]axles[/COLOR][/COLOR][/COLOR]....and still it vibrates. They gave it to me today to try...and it's actually WORSE! Now I get a high pitched drone and vibration at highway speeds. Enough to cause the panels in the rear to vibrate! Again if I take the load off by lifting the pedal the noise and vibration go away. So I'm bringing it back tonight...with some suggestions I thought I'd check here first:

1. Maybe try swapping the rear axles? I remember once hearing that CV's can wear and cause vibration before they start clicking...and that they wear obviously in one direction.

2. If that fails perhaps I need a rear diff? Has anyone gotten "under load vibration" from a failing rear diff???

Any other ideas? I'm getting desperate...and I'm running out of cash!!

Steve