okay, i have a 2001 ford f-150. i would like to hook a sub up in it. but i have a few questions. i dont want to buy a new stereo, is it possible to hook a sub up to the stock stereo in my truck? also, if i did that would you atually get any "thump" from the sub? or would i need to add an amp? i want to do this the cheapest way. please help me