Mysterious front end rattle

[carey558899]

Hi, hoping someone can suggest what the mysterious front end rattle/clunking is that has evaded 2 mechanics and several attempted fixes! The symptoms on my 2002 Boxster S are:
- dull rattle that sounds like a "loose coupling" or a "bucket of large bolts"
- seems to be from the front and occurs when the front wheels hit a bump
- most noticeable at low speed (30-40kph or 18-24mph)
- most noticeable when driving over low but "sharp" bumps/cracks (e.g. bridge expansion joints or large cracks in the pavement)
- only occurs in warm temperatures (above 15C or 62F), and even then usually not til the car has been driven 15-20 minutes

Have replaced both front sway bar links and the right front lower control arm, but no noticeable improvement. Was led to believe by the first mechanic that I should now change the left front control arm, but the second mechanic disagreed after listening to the rattle and doing the "fender push test". Hearing the sound (while driving), he was in fact surprised that the first mechanic suggested it was due to the lower control arm. After putting the car up on the hoist and prodding the suspension components, he was unable to find anything abnormal.

Any suggestions or advice would be much appreciated as this is now driving me crazy! Thanks!