Been there, heard that.
The first time it happened was in the wee hours of the morning, scared us to death and we about killed each other jumping out of the bed. There lay Bubba in his bed beside our bed sound asleep, head in the air and howling. He put his head down, never opened his eyes, and continued snoozing. We just looked at each other and cracked up. He did it several times over the years. We still haven't heard the first day-time or night-time aroooo from Bogie, but he's only 1 and 1/2 years old.