Jolts/jumping Of Front Of Car On Steering

[amok2]

Hello,

Just developed a problem with my 04 2.0 petrol avensis t3-x.

When moving with the steering near to or on full lock, then the the front of the car seems to 'jump/jolt' as though a front wheel has gone over a goldball sized stone.

Most noticeable when reversing on full lock e.g. reversing through 90 degrees produces 3 'jumps/jolts' which can be felt through the steering

At first I thought that there were stones on the ground, but this is not so!. Happens especially when car is left overnight, and being used first thing.

Dealer changed both front rubber 'shocker tops' but this has made no difference.

Anyone had this problem , or know what it could be.

Something not right for sure.

p.s. when I took car for service around 9 months-year ago, they may have changed steering rack under warranty (even though not an electric steering model to my knowldege), but there was no problem immediatley after this (in case something was mis-fitted at th time).

Thanks

Amok