we have a 2000 6.0 2500 4x4,and when its cold there is a buzzing noise coming from the fuel line area under the seat area.whats going on here,is it going to let us down soon? fuel pump,filter? goes away when warmed up.truck has about 55k miles. oh and a lot less guts than the duramax,ha!

If the filter has never been replaced, do it. They should be done every 30k or sooner. Pumps are not uncommon around that model year, though.
Be sure it's a fuel system noise, and not something else before pulling the tank, of course.