My 2004 hemi ram 1500 knocks when i start it up! could this be my oil sending unit?

Check knock sensor ,if it don't have knock sensor change cam shaft sensor.

take out bolts, and the crossmember. if its 2wd, it doesnt get much easier. Be sure the oil pump pickup is clean, these engines seem to sludge up, use a good quality synthetic oil like Mobil1

the oil pressure sending unit is by the oil filter and they are very easy to replace about 30 minute job

Is this a knock or clicking sound? Hemi's are known for breaking exhaust manifold bolts and causing a clicking sound which is a exhaust leak.

Sounds like the oil pressure sending unit needs replaced.

Rings & bearings & oil pump need urgent attention!
Cheers Rob

Slide a large piece of cardboard under the truck after driving for ten minutes note in which area directly above the spot on the cardboard the oil is coming from then get under the vehicle with a drop light to look for the origin of the leak, if no leak is detected then it may be the engine is burning oil this could either be valve stem seals or broke or worn oil rings.

2 knock sensors are used..small black plastic sensor bolted into engine block below each exhaust manifold..be careful not to over torque bolts upon installation

oil pressure sending unit could be bad.

take it to autozone they will check why the light is on for free