[thstone]

Once the engine (and oil) is warm, a 5w40 oil should have more than enough viscosity to protect the engine (its not likely "thinning out" unless your engine temp is over 250). Changing to a 10w40 will not likely improve the viscosity (its 40 in both oils when warm).

The first thing that I would do is to have your front engine mount inspected, its probably worn out and making a knocking noise.