I have this too on all wheels. On wet roads the car is quiet, when warm and dry it creaks and groans like an old sailing ship (and drives me nuts!).
I'm certain that it is the polyurethane bushes. I've just bought some factory original rubber bushes to replace them (not fitted yet). It costs about $900 to replace every piece of rubber in the suspension including the anti-roll/sway bar bushes using original parts.
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