Engine roar and loss of power...

Driving home from work Thursday at around 30mph the engine suddenly became louder and had me thinking that I'd slipped out of gear. From this point onwards the engine has sounded progressively 'growlier', performance has declined and the engine has cut out twice. Seems to me it's probably an exhaust leak close to the engine but I haven't been able to find exactly at what point. Back to the dealer Monday for the fourth time since taking delivery 4 weeks ago....