Residents living near Queens Park in Bolton reported hearing a repetitive "loud tapping" in the early hours this week leaving council officials baffled.
One resident even recorded the sound, the Bolton News reported.
Police officers called to investigate "suspicious banging" eventually traced the noise to construction work on a nearby railway line.
Complaints began on Monday 28 November with the sound being heard for up to four hours a night.
Bolton Council, which runs the park, said it had "no idea" where the noise was coming from.
"We don't do anything in the park at night," said a spokesman.
Greater Manchester Police said they were called at 04:08 BST on Tuesday by a resident on Mayor Street who reported "suspicious banging" in the park.
"The noise was traced to industrial work being carried out on the railway tracks.
"The incident has now been closed."
The Bolton to Lostock railway line runs just south of Queens Park.
A mystery surrounding a "banging noise" heard coming from a Greater Manchester park at night has been solved.