Why do I have a gross smell coming from my ac vents

I would first start in changing your cabin air filter. Dirt and mold build up in them over time. When was it last changed? They should be replaced every 15K miles. If that doesn't work, then the condenser might need to be cleaned. I always turn the AC off before I turn the vehicle off and or park to bring in fresh air to warm up the condenser to slow down the mold growth. You can report back if need be and we can give you a way to do the cleaning

Dead mouse?