The problem is this - the vacuum cleaner started to whistle like an airplane. We struggled and thought something was stuck and created a whistle effect. Washing the filters and all that - didn't help. During use, it could get a little better. But this sound scares the cats and might scare the neighbors. So we started thinking about buying a new one. One day I decided to google - "Rowenta vacuum cleaner whistles" and immediately found several videos. The problem is common. The essence - the seal on the filter has dried out and it becomes a kind of whistle. The moments when the sound got better - most likely this interval was just clogged with debris. So the solution - to glue the seal. I didn't have anything like that on hand (like what they stick on doors or windows). But I had double-sided tape (the thick kind, maybe it's some kind of double-sided seal).

A little work with scissors - and the problem is solved. I was even a bit surprised.