Rumble noise after tune up and smells like gas?

I had a mechanic (he is a friend and works at a repair shop) do a tune up on my 2004 Chevy Malibu V6, I got the car back yesterday morning, and while I was idling in the parking lot, I noticed it was making a rumble noise (it almost sounds like a faint helicopter) I got out of the car to here where it was coming from and it is coming from underneath my hood near the windshield on the driver side. I don't know too much about cars, but I know my car was not making this noise before. Also, about half way through the day yesterday, idling again, my car starts smelling like gas, so every time I was driving it yesterday, after I would stop at a light, it would smell like gas again. I have never had any problems with my car before. He said he replaced the plugs, wires, a filter, and cleaned something out, I want to say the Fuel Injector. He told me it was nothing he did during the tune up, I just didn't notice before because the car wasn't running 100%. He then said when I drove it to him he could hear an exhaust leak, which I pay very close attention to sounds, and never heard anything before. Any help on this would be appreciated!