Rattling Noise
 

I have a P5 with about 80k. For some reason, it starts to rattle when I'm in gear. I don't know where it's from, it sounds like somewhere in the front of the car, but Idk where. The noise is especially loud when I'm going slow in a gear, for exapmle, if I shift into 2nd while going 5-10mph you hear it pretty loud. The worst is when I go uphill, i'll be in 1st and no noise, but the split second that i switch gears, the noise comes and stays for a few seconds till I pick up some more speed. It only happens when I'm in gear, never in Neutral. I never changed the tranny fluid, which i konw i probably should do. could that be it?

And it happens even after the cars warmed up.

Any Ideas or just go to mechanic?? Thanks.