Stick with synthetic, that rep is an idiot. Please don't fall for any type of "fluid" flush unless you know what you're getting done. These guys will sell you everything on the list if they had the chance.
Read the manual. It has everything that says what needs to be inspected or replaced. For the most part, you won't have to do much exept oil changes and air filter changes.
The issue with the noise could be a lot of things. Is the car 100% stock? Did they inspect the exhaust system? Did did run a diagnostic? if so, any codes?