Water circuit sporadically empty at ECAM 556.55

Hello,
I have an ECAM 556.55 MS Prima Donna. The machine is just under 2 years old - so still about 2 months warranty.
For a few weeks, I hear a slurping sound when switching off, when the brewing piston moves back and forth, as if I suck a glass empty with a straw.
Then every now and then when I turn it back on, the message Insert water spout - water circuit empty comes on. When I flush with the water spout, water comes immediately and it doesn't seem to me that the pump is restricted. Coffee and milk dispensing are flawless.
Normally I would have sent the machine immediately, but that it can be that the error message also times 4-5 days does not come at all. With the DeLoghi service the machine will most likely come back unrepaired (what one hears so).
I have already exchanged pumps on similar machines in the past. Repair experience is available, have the machine only not yet made on, because it is still under warranty.
Does anyone have a tip?
Thank
youGreetingsAndré