Low frequency squeal from front suspension
 

Occasionally, whilst manoeuvring my 2002 Boxster s - usually whilst parking or driving slowly without the foot off the throttle and on full lock I get a really horrible "low frequency rubbing, grating squealing sound" coming from the front near side inthe area of the disk. It is clearly wheel rotation associated, I can find no play or movement on any of the suspension points whether loaded or jacked up. I replaced the front disks and pads less than 5k miles ago. I also notice an amount of vibration/play when slowing from high speed which I associated with wheel imbalance. I have since had all four wheels balanced but still have the vibration coming up through the steering column on braking.
Any ideas welcome?