Now here is something worth looking into:
http://www.space.com/scienceastronomy/ap_huygens_update_050127.html
"Based on data collected by Huygens' instruments, Sushil Atreya, a professor of planetary science at the University of Michigan in the United States, believes a hydro-geological process between water and rocks deep inside the moon could be producing the methane.
"I think the process is quite likely in the interior of Titan," Atreya said in a telephone interview.
The process is called serpentinisation and is basically the reaction between water and rocks at 100 to 400 degrees Celsius (212 to 752 degrees Fahrenheit), he said."