'04 XJR: Squeel under Acceleration

I've noticed my new-to-me '04 XJR produces a brief squeel (maybe 1.5 seconds) at the rear when I punch the accelerator.  It happens when I am underway (and it is definitely not wheelspin) at highway and side road speeds (I have not tried to punch it from standstill).  Do they all do that or is this a driveline issue I need to get checked?
 
Thanks,
 
Steve

Is it a squeek or is it moreof a hoot. Does it happen when you punch it and trans drops a gear to accelerate? If so there is an additive to put in trans fluid. Dealer only. Drain out 1 litre of fluid and put in the new litre of additive.

Thanks FJT...yes it is more of a hoot. 
 
Steve