Firstly, sounds like you've just changed the oil. Do you knwo what grade oil was in the engine previously? 5w40 is a godo grade but a bit thin so if you're comming from a 10/15/20w??? grade the extra noise can be expected.i've just used carlube fully synthetic oil 5w/40. thats the oil the garage recommended.
I don't recall the name and not sure what other members views are regarding this method but it used to rectify the problem:confusedIt would be a good idea to Auto-Rx your engine. Find a Group III synthetic oil to run with Auto-Rx that meets ACEA A3