Squeaking sounds you hear is plastic rubbing together as case flexes indicating case is not rigid. This can be bad as case flexing can break glass screen when carried to exstreme. Kobo mini uses 6 screws in addition to plastic clips making it a little more rigid and the silicone rubber would also help. Regardless screen glass is thin and easily broken.
He is referring to Silicone Rubber RTV Sealant. Comes out of tube about like tooth paste and cures to rubbery like substance. Listed Wikipedia links as they often available in many languages. (RTV means Room Temperature vulcanized.)
http://en.wikipedia.org/wiki/Silicone_rubber
http://www.amazon.com/Permatex-80050.../dp/B0002UEPVI
http://en.wikipedia.org/wiki/DAP_Products
Loctite