I hope Dana left out a work in his description of the smell you're getting. The last time I smelled hydrogen was just before I got off of the Hindenberg. I'd check for a minor coolant leak in the heater box. Hot antifreeze has a distinct odor.
OK chem nerds. PURE hydrogen has no smell at all. Cats don't smell quite as much like rotten eggs as they did 20 years ago, so maybe that's not the issue. Engine coolant, polyethylene glycol, doesn't smell anything like a beauty shop to me. Maybe there is a natural gas leak near where you park your car.