There is a recall on 2012 mazda 6 , Here is what I would check out .
MAR 11, 2014
2012 Mazda MAZDA6
Mazda North America Operations (Mazda) is recalling certain model year 2010-2012 Mazda6 vehicles manufactured September 14, 2009, through May 2, 2011, and equipped with 2.5L engine. In the affected vehicles, spiders may weave a web in the evaporative canister vent hose, blocking it and causing the fuel tank to have an excessive amount of negative pressure.
Negative pressure could cause the fuel tank to crack resulting in a fuel leak, increasing the risk of a fire.
Mazda will notify owners, and dealers will reprogram the powertrain control module and inspect and clean the canister vent line. If a web was found in the line, the fuel tank and check valve on canister vent line will be replaced. These repairs will be done free of charge. The recall began on April 30, 2014. Owners may contact Mazda at 1-800-222-5500. Mazda's recall number associated with this campaign is 7214C.
Potential Units Affected:
Mazda North American Operations
Read more: http://www.motortrend.com/cars/2012/mazda/mazda6/recalls/#ixzz3A3gO2Ac1