Why is this happening?!!Please help.

I doubt the hill had much to do with the problem since even a steep hill is a fairly small angle. Acceleration and the resulting sloshing might, but 1/4 tank should keep the sock covered. That is a problem in my Newport with TBI, but only when ~2 gal, and should be much less problem with a carburetor. There are no baffles in my factory 65 tank. I looked inside with sun shining in the other hole, looking for rust. There is a tank vent, at least in my 65 Dart it is a small tube off the fill tube that loops up in the trunk then down thru the floor seal. A common problem is that stuff like undercoating plugs the vent exit.

The rapping sound is probably on a belt-driven accessory like the alternator or water pump. Usually when a water pump bearing goes, you get a coolant leak. Do you have power steering? The bracket on my 69 slant cracked. I don't recall much sound, just noticed the pump moving around too much.