For the past three nights I've been awake between 2:30am and 4:30 am and have heard a strange low frequency hum that is continuous for those two hours. During the two hours I also hear helicopters that come and go but those aren't constant. I'd say the helicopters can be heard for 10-15 minutes at a stretch. The hum sounds like it is in the sky but I can't be sure. Has anyone ever heard anything like this? What could it be? Maybe chemtrail activity?

I am in central California.


I've often heard this hum. I am in Central California as well. I always hear it more intensified right before a major military action.