Yes. It's a propeller spinning in the water.

kek i just checked that out because i didnt know the answer, its a massive paragraph i wont copypasta but the opening is enough to give you an idea of where it goes -

During the year 2000, an unusual meeting took place with a next door neighbor (Francis 'Frank' Smith) of the then HMAS Stirling Naval Base commander. He was an Aircraft Maintenance Engineer (originally trained at Government Aircraft Factories Fisherman's bend) who had been aware of the fluid dynamics issues of the Collins class for some time, purely by interest and observation on television. After a lengthy discussion, he was invited to discuss and demonstrate where possible, his observations at the Stirling Naval Base with Navy and Defence Science and Technology Organisation (DSTO) staff who were there at that time as part of an investigative group. He showed on a white board...

tl;dr nosey aircraft engineer neighbour of Naval commander solves submarine noise.

Apparently tho, the US/Russian sub detection gear is that dialed in to each other the Collins class was still able to fuck with the USN during excercises