Actually -
This is the 3rd car I have fully poly bushed the suspension on, and the first I have experienced internal vibration.
I have also partially fitted poly bushes to 3 of my other cars without vibration.
Only vibrations experienced with bushes were:
Ice hockey puck rear engine mount on my Mk3 Valver - works for the front mount, does not work on rear
OEM style Mk4 R32 solid rear control arm bushes - on older Golfs - this vibration dies down after 100 miles of driving.
The poly Dogbone insert appears to be a popular modification on the Mk5 - still wondering if this vibration is normal, or something else worn or even if it will go away after putting some miles on it.