What causes my 1997 Renault Scenic to smell like 'cat's pee' It's as though some fluid is dropping onto the hot exhaust pipe but no sign of a leak when parked?

The odor that smells like cat urine could be coming from bacteria that grows on the A/C filter and/or in the ducts. With the A/C off, turn the fan on high and spray a water-based deodorizer into the air intake. Use a spray bottle, not an aerosol can. Next, turn on the A/C with the fan still on high and spray some additional deodorizer into the air intake. If this doesn't completely get rid of the smell, try replacing the filter. If this does not solve the problem, the smell could be coming from a bad heater core.