BMW Repair: 2003 BMW 525i, 2003 bmw 525i, sitting in the back seat

Question
2003 BMWi Vin: WBADT43453GY99350
85,000 Miles

my car moves (shakes) side ways. The rear seems to move in a wagging motion (left to right)at any speed but the steering wheel does not shake. This problem gives you the sensation the wheels are coming out. The tires are correctly inflated and there is no unusual wear and tare of the tires.There is no warning lights on at any time.The dealer's mechanic who looked at it said there is no problems that he can see or feel.The car was road tested buy the same person. I also notice that the people sitting in the back seat feel it more than the driver. I hope you can help us
Thank you for taking the time to take my question
Sincerely,
Lorenzo

Answer
If the dealer's mechanic didn't feel anything unusual, it may be that it's something you're not used to.

Only thing I can think of is your tires.  Are they a lower grade tire that tends to walk more?  Sounds almost like a snow tire syndrome.

As a thought, go drive a different 525i.  Find a different dealer, one being sold by a private party, etc.  Maybe you can determine if it is your car specific.