Other than cost, there is no downside to using synthetic motor oils.  Most new cars actually require this due to the fuel savings of using thin oil while offering lubrication at high temperatures -- attributes that are best achieved using synthetic.  The other upside is they lubricate better and therefore the time and miles between changes are typically double vs. fossil lubricants.

That being said, changing to a thinner grade oil or extending the time and miles between changes on our engines is NOT recommended.  Insofar as making things more quite, since the majority of noise in our engines is not related to lubrication, I'd be surprised to hear that changing to synthetic makes a difference.  But I'm always open to ways to reduce the clatter.....