If you want to spend money you can pull it apart and have the crank turned. I think you can but I seem to recall something about these having some sort of special treatment that will be taken off if you turn the crank. Otherwise you can drive it till it blows up then put a good used engine in. Or, put the good used engine in now. This usually happens when they get ran low on oil. Not enough to lock it up but enough to take out a rod bearing, usually #1. I have ran across many cars over the years sounding exactly like yours.