By GLE is this a 16 valve engine? If so, the valve cover (engine top) will say so, and run right away and get the timing checked out. See FAQ for weaknesses regarding this. If you neglect it, you will have an engine head to rebuild and cost you thousands...

The rumbling is usually to a poorly aligned center drive shaft, or worn out center supprt bearing.

White smoke? Even when hot? Are you sure the smoke is not blue? Given the poor cylinder compression you might have a slightly leaky head gasket. This would explain the smoke, and poor driving conditions. Get it fixed fast if you want your engine to survive. Pull out your oil dipstick and see if you see and refrigerant (coolant) on the stick. If so, then you have coolant in your oil.

You problem in whole do not look like you can leave them be, should be checked out right away.

Greg