I was in my washroom drying off after a shower and I heard something funny outside. About 5 minutes later, I noticed the funny noise was changing pitch as if through a chorus effect. I only caught the tail end of it but the noise lasted a good 6 or 7 minutes. The chorus effect is barely noticeable in this video but what you can hear is individual trumpets/flutes coming in and going out. He reports that 'trumpet/flutes-like' noise lasted 6-7 minutes: