The tapping noise has been very annoying. This is my second posting on this subject and I have read about the lifters noise on these engines posted by others. I replaced my engine mounts, changed gas brand, run engine cleaners to get ride of carbons, etc. and my E500 still sounds like a diesel. I showed it to two dealerships and the same ansewer, it is normal for this engine. Several MB shops have recommended I go with a higher viscosity oil, 10w-40. I don't mind going with 5W-40 but not sure about higher viscosity. I have 80,000 miles on the car and live in Dallas ( Local temp ranges from 30F-110F). Should I try it? Has anyone done this? Do I damage anything? please offer your ideas. Thanks.