Usually, when a Remington 700, or, any other rifle fires on it's own when the buttstock is bumped, it's an indication that the trigger has been messed with, which if true, will usually void any warranty. The problem may require a simple cleaning and adjustment which can easily be done outside a factory setting by a competent gunsmith. However, if you wish to contact the company, here is their info.
http://www.remington.com/pages/our-company/our-company/company-info.aspx
