De Longhi Magnifica S faucht / zischt / gluckert

Hello!

recently my De Longhi Magnifica S has been making unusual noises - at least I had never noticed them before. I would describe it as a hiss, hiss or gurgle. And it almost always occurs just before coffee runs or before water runs during the rinse cycle (on/off). I've put together a short video so you know what I mean:

Sometimes the noises last longer, sometimes shorter, rarely they don't occur at all.

I'm a little worried that the machine might give up the ghost soon. Does anyone have any ideas what the problem could be? Is there air in there somewhere or something leaking?
I honestly have no idea where to start. But would like to react before something breaks (hopefully I'm not too late).


A few more clues or info:

All functions otherwise behave normally and the coffee tastes as good as before.

As far as I can see, there is no water leaking anywhere. There is no significant amount of water under/next to the machine (a few drops here and there, probably because I'm not always very careful when filling up with water). There is also no water in the small red drip tray (there was water in there for the first time ever a few months ago, but not since).

Recently I had an error message:
coffee grounds container and warning triangle flashing, water jug on (= grind too fine OR air bubble in circuit if water softener filter present [don't have one]). After switching off and on the error was gone again and has not come since. However, the noises were already there before.

The noises do not occur during the output of water or steam through the nozzle head, as far as I can tell (but I also don't use it that often). There is also a hissing noise before steam is dispensed, but that is normal or has always been the case.

We have ultra-hard water of 22 DH. I don't use a water hardness filter, but only water that has previously passed through the BWT filter for extra hard water(BWT Soft Filtered Water Extra) goes into the machine. This works well and I also don't have to descale the water filter more often than in previous places of residence.
I always descale the machine immediately after being reminded by the machine and with the Durgol special descaler. The hardest water hardness is programmed into the machine.


I am very grateful for all tips and advice!
Have a nice evening.