Clunk/vibration when reversing on full lock

[mrsmr2]

When reversing out of parking spaces with full lock, there is a bit of vibration from the front wheels and it feels like one of the wheels is running over stones.

I've had a search on here and seen responses ranging from spring issues through to worn front tyres skipping, so I'm not much wiser really.  

Other info that might help:

My front tyres are near the end of life but they don't need replacing yet, rears are on the wear markers (so all 4 will be replaced soon).  
There is a slight feeling of lightness in the steering when applying full lock going forward.
Alignment was checked one year ago but as the result showed everything was within tolerance I am very suspicious about the result.  My car has always needed something adjusting every couple of years with past alignment checks - nothing major but there is always something out of tolerance.
This vibration started about 6 months ago.

It'll be serviced next month and I'm doing a North Weald day in three weeks (should be fun with those rears) so I want to work out if I have a problem before either of those events.

Thanks

[jonbill]

Are you sure it's not the rears? Maybe the LSD is causing it to skip.
Other than that cvs show their wear most at full lock.

[mrsmr2]

Sorry for late reply.  I don't think it's the rears.

Could be CVs.  Car has only done 44k though.

[StuC]

How is the steering UJ looking?