Alright, so I dropped it off at the dealership Thursday afternoon to leave it overnight. That way they could hear it when it was cold this morning.
They heard it! The service writer called me at 8:30 and said it sounded horrible and they are fairly sure it is the speaker itself. So they ordered the speaker and amplifier just in case both are bad, which is a possibility.
The best part: the car is not under warranty. However the service writer said that he is going to see if GM will "good will" warranty it and if they don't the dealership will pick up the tab!! Yay! The parts are going to be in Monday, so I opted to leave the car there until then...so he even put it in the shop this afternoon so it didn't have to sit outside all weekend in the weather. I love my dealership.
