It's described as a booming or thumping sound. A repetitive, dull bass that been pulsating through homes and rattling residents' nerves.
It's music whose origin is a mystery and has been bombarding residents in the Delaware River towns of Carneys Point, Penns Groveand Pennsville. It's been heard various times since the summer, some say, but the worst spate has been in the past couple of weeks.
"It was like a sickening pulsing heartbeat. We turned up our television, but could not overpower the throb," said Monica Morris Lind, a riverfront resident describing the wave of sound that was traveling across the water on Sunday night.
"The thumping came straight through our front porch to the back of our home in the kitchen. It went on until the wee hours of the morning until around 3 a.m."
Is the First State having a party and forgot to invite Jersey?
That's one idea that can probably be ruled out, but others have theories.
A party boat? Music being played on a dredge anchored in the channel? A nightclub on the Delaware shore?
It begins usually in the early evening and continues on into the early-morning hours. Sometimes that's as late (or early, if you will) as 4 a.m.
Residents are aggravated. Police are frustrated. Their patience is wearing thin.
"At this stage Delaware authorities have not been able to locate (the source of the music)," said Penns Grove Chief of Police John T. Stranahan Sr., adding, "We've had officers, including myself, go to Delaware to attempt to locate the music and we've narrowed it down to a very small area."
He wouldn't yet specify where but promised once it's confirmed he'll let the public know.
"Everyone assumes its local because it's so loud," the chief said.
Carol Napoleon Hampton of Pennsville recorded a video of the weird occurrence Sunday evening. From a spot south of the Delaware Memorial Bridge the music can very clearly be heard over the sound of river waves lapping the shore.
Residents for a 15-mile stretch north and south of where Hampton recorded sound describe it as loud or louder than what she captured. They say they not only hear it, but can actually feel the vibrations from the music rattling their homes and their bodies.
"Some nights it's been very loud. Sometimes it's just bass off in the distance. However, still annoying," a member of one Facebook group in the Penns Grove-Carneys Point area described it.
Others have said they thought a car was parked outside of their house blaring music, the sounds have been so loud.
Pennsville Chief of Police Allen J. Cummings said his department has received more than 20 complaints in October alone.
Delaware authorities, he said, told him "they are working on it."
Carneys Point Police Chief Gerald R. Krivda said his department has received numerous complaints which were passed on to Delaware.
The county's 911 call center has received at least 55 calls about the music in October, the center's director, Scott Haines, said. The largest number of complaints came in on Oct. 20 and 21, 38 in total just that weekend.
A spokesman for Delaware State Police said so far they have received three noise complaints -- on Oct. 14, 23 and 28 between 7:45 and 11:30 p.m.
Master Corporal Michael Austin said the area identified by callers stretched from the Port of Wilmington north to Edgemoor Road -- areas across the river from Carneys Point and Penns Grove.
Austin said when troopers went to the areas they heard no music and were unable to find a source.
He said police were told a possible source of the music could be a barge in the river connected to dredging operations and the Delaware Department of Natural Resources. Officials there didn't immediately respond to an inquiry sent by NJ Advance Media.
And it's not just people living along the Delaware River who are hearing the mystery thumps in the night.
Residents far inland in Mannington Township and the village of Auburn in Oldmans Township have reported hearing the bass sound late into the night.
One theory is the music is coming from people gathering in Delaware and showing off the enormous custom sound systems in their vehicles.
That was the case this past summer when booming music coming across the Delaware River from South Philadelphia was keeping residents of Gloucester City awake.
Austin says New Jersey residents hearing the music and who want to register a complaint should call Delaware State Police at 302-573-2800.