Yesterday evening my AC was working fine, I left the house and a few hours later I returned and noticed a loud sound, almost like a trumpet, coming from my outdoor AC unit. Not sure how long the sound was going on while I was gone, but a few minutes after I got home the sound stopped and I noticed my house was much warmer than it should've been. I went outside and looked at the unit and heard the fan running, not sure about the compressor (didn't know enough to listen for it). This morning I woke up and immediately turned everything off for a couple hours. When I turned it back on, I heard a buzzing/humming sound. Neither the fan or the compressor were running, but the fan started up after I poked it with a tree branch. I tried feeling the two pipes coming from inside, one felt cool and one felt warm, but I'm not sure if it's from when the unit was working yesterday. Any ideas? My furnace is only 6 months old, and my house was built in 2001, so the outoor AC unit is no more than 9 yrs old.