2009 Macbook Pro significantly heavier than 2011?

Hey everyone,

Bit of a weird one here, but my girlfriend has a 2009 13 inch Macbook Pro, with a 2.4Ghz C2D and a 160GB hard drive. I have the base late 2011 version, with a 500GB hard drive and all the newer shizzle that comes with it. Weirdly, her Macbook feels a lot heavier than mine. It could be just me, but are there any factors that would somehow make it heavier than mine? Mactracker says that they should both weigh the same...can anyone shed any light on this?