Well do a visual inspection of the suspension and the motor/trans mounts first. If you are saying it comes from the front of the car it could very well be a motor mount, or more likely I would say a broken pitching stopper which bolts to the firewall. You dont by chance hear this clunk when you go over bumps do you? I was thinking a strut or an upper strut mount. How many miles are on the vehicle? Do you notice the vehicle not holding boost or anything?