Was the Whisperwalk installed or was underlayment foam installed? If 'cork' as I know it was used as a 'subfloor', you're out of luck with doing a quick-fix. If a pro installed either the Whisperwalk or the underlayment foam, call them back (although you did say 'you' installed the Pergo). Case closed. If YOU did the work, then it's possible (and I want to emphasize possible) that the install was not done properly. Neither the Whisperwalk nor the underlayment foam should squeak.
Assuming you have the Whisperwalk or the underlayment foam installed, is it possible that the sub-floor is squeeking??? What are the 'layers' between the joists / concrete / whatever and the Pergo itself?