Background noises in 739NG?

Using the 737-900 for the first time from cold and dark. I’m on stand in JFK and there’s this really weird like thudding/tapping noise in the background. It’s not my iPad because it’s brand new and it doesn’t do this with any other aircraft. Is it 737 specific and if so what is the source of the sound?

Hi Jan,

The sound appears even in cold and dark, it resembles tapping of footsteps…

I’m not sure if this video will send but I found the same thing in it

The very start when the camera is panned around the aircraft it has this distant thudding/tapping sound, and since it’s a YouTube video I know it’s not just my sim or speakers..

Edit: I have no idea if anyone else is going to hear it, on the old iPad or iPhone it makes no sound but on the brand new Air it does 🤔

Quote from Jet-Pack (IPACS)

Is the sound of the trim wheel perhaps?

no its there even when the aircraft is cold and dark and disappears when the engines are started. i think it might be specific to the 739NG

Quote from czolgu

I have the same thing with those noises and made already a thread but it wasnt taken serious, it can be heard on ipads becuase the have good bass speakers and that steps are haunting me since the begining

Okay good so im not the only one. Where does it come from?