X3 Poor Transmisson due to Tyre Treads

[keitht]

Help required. I own an X3 which has brand new bridgestone tyres on the front and 6 months old pirelli tyres on the back, both the same size. When the car comes to a stop I get a noise/transmission jolt. It almost sound like the hadbrake has just released but I'm 100% sure this is nothing to do with the handbrake. This happens much more frequently in first or second gear as the car is slowing down. The local BMW dealer have said that this occurs when there is a differential between the front and back tyres. :confused:

Does anyone know if this is true as I'm worried about long term damage to the transmission.

Also if anyone knows how to overcome this problem I'd appreciate your response.