a/c not working/strange noise

My 97 T & C's air conditioner quit working - the heat is fine, it's winter so i'm trying to hold out - but - there's this wierd noise, like a phutt-phutt-phutt, mixed with a high pitched shriek, when the car is idling, going downhill, or in park with engine on, when i press on gas pedal the noise goes away. Any ideas? thanks

Get the vehicle checked out. Its possible the compressor is on its way out and/or the belt tensioner is worn.