Two weeks ago I purchased a 2011 Buick LaCrosse CXL. I love the car and the ride is great. However,every morning and after I crank it up to go home from work it makes a loud buzzing noise upon start-up. It eventually fades away but I'd like to know what it could be? Has anyone had this issue? Could it be the fuel injection? It's still under warranty and I'd like to get it fixed before it wears off. I took it back to the dealership and they kept it over night but they couldn't hear it (or so they say). All suggestions are welcomed.