Engine sound and choice of oil

[pathan]

My MB dealers have suggested that if they replace the engine oil in my S500 Model june 2002 ( 9000 miles) with a totally synthetic oil, ( present oil is Semisynthetic) the engine will run quieter.
Could someone please comment whether they think that this is a valid thing to do or whether the dealers are pulling wool over my eyes or ears!
Shall be grateful.