Easy.

For a number of reasons- the load which usually is absorbed into the shocks is being transferred to the surrounding chassis and bushes. Lowering springs, stiffer springs, bigger swaybars and new bushes can all do this to an older chassis.

Or , the most likely reason is the team installing your new shocks, tightened the fork and control arm points while the suspension is uncompressed. IE car off ground.
This will cause the bushes in the control arms to overly stretch / contort beyond normal movement and thus "creak".