Ditto and, unfortunately, there's no way to prove that they did the damage as it will be your word vs their word. I'd certainly not return to that shop and if (after you show them the dirt/rocks under the hood, etc.) they won't cooperate - Yelp the heck out of them and expose their incompetence....Even before investigating the sound change, I’d come completely unglued if a shop drove my car, much less sufficiently enough to get direct and gravel all up in it. That’s the first order of business.
Welcome to the forum and sorry to hear about your troubles...I'm with Ringmaster, no one touches my car except me and (my trusted Shelby co-owners)!