#1 don't goto a stealership
#2 grab a stethascope or simliar and use it to determin EXACTLY where the sound is comming from. you can get one fro like 5 or 10 bucks at a cvs/wallgreens
#3 does the sound increase as the rpms increase? what about if you turn on the a/c etc.?
#4 if you must take it somewhere ask friends/family for a good mechanic. then look themup online and see if their are any reviews about the shop. just because a person reccomends it doesn't mean it'* a good shop. my grandma went to the same shop for 30 years and was ripped off for 30 years. like the one year old tires had dry rot etc.
#5 a dealer will cost you alot more for a diag then a mechanic will. my mechanic does it for free. though i havn't used him in years as i turn my own wrenches as any proper man should. but he will tell me whats wrong
good luck! let us know how it turns out.