People in Philadelphia heard some strange sounds earlier this month. Several have uploaded recordings onto YouTube. Here’s one from YT user ‘buttadee‘:

Here’s what he or she wrote about the experience:

This is the strange noise I’ve been hearing periodically over the past couple of years. Occurrences have been frequent lately, and I notice it tends to happen before and/or during rain and other impending weather warnings like snow storms. This video was taken outside my front door after 2am on March 4th. I starting hearing it tonight around 6 or 7pm and thought it was just helicopters, but the sound never faded. It’s hard to pinpoint where the noise is coming from. No aircraft in sight. Doesn’t help that it was overcast.