Regarding bumpers, no matter how you spend money and energy on the bumpers, the paint will eventually peel off. I have already discussed the option of putting rexene over it in my previous posts. It is far better solution!
The link to reading codes is mentioned on the top post above. As far as the sound is concerned, there could be many reasons for such sound including head, crank, water pump/water body bearing etc. As per advice of your mechanic, you can start with the diagnosis from the engine head.