Really annoying squeak 206 1.6XSI

[isisalar]

Got a lovely 1.6xsi 206 for the wife a couple of weeks ago, 05 plate with 52,000 miles, had it checked over by BL autos and all pronounced good, the only weak points being the rear discs and pads may need changing before long and the tyres were not brilliant, rear suspension I know is a weak point on these but it's ok. Got tracking done and a new set of tyres fitted last Saturday and ever since there's been a squeak which sounds like its related to the suspension ie. it happens going over bumps. have only heard it whilst going slowly.The mystifying thing is that it disappears after the car has done about 2 miles and doesn't return until the cars been standing a while and starts another journey.
BL auto's suggested greasing where the tailgate catch sits on the body and that's made no difference. It's not loose wheel nuts either. Can't seem to reproduce it if the cars stationary.
Any suggestions? The first time I heard it was taking the car out of the tyre fitters so this may be relevant. Alloy wheel mating face?
Other than this we're really pleased with it so it would be lovely to get it sorted.
Cheers
Paul