A while back I e-mailed A-Star product support about my noisy SMX and SMX+ boots. Here's their reply:
Thank you for contacting Alpinestars.
The reason for the squeaking is at the rounded ankle plastic which covers the ankle bone sometimes it is so smooth that it rubs together with the plastic underneath and causes it to squeak. A quick solution to the problem is to use sand paper to roughen the surface between the rounded ankle plastic and the plastic directly underneath. Simply lift the ankle plastic up a little and sand down the plastic. The rough surface when it rubs together from walking will not squeak.
Try this tip and if we can be of further assistance please feel free to contact us.
Torrance, (CA) USA
Ph: (800) 727-8277
Fax. (310) 891-0299