Work Colleague's Habit

[nutellasandwichesandprosecco]

I work in a small office of 4 (we're within a company but our department has it's own side office). We're 4 women and all get on really well and I really enjoy my time with them. Three of us are 40+ and we have a younger colleague- she is 27- she's really lovely and is good at her job and I am really fond of her and she has done some babysitting for me on occasions so I know her well. The other two in the office get on well with her too. They are becoming quite irritated by her though as she constantly sucks her thumb. She sometimes makes a sucking noise and occasionally will dribble whilst doing it. I've been aware of it since I met her- I find it a bit difficult to deal with but am mostly used to it now and accept that it's just something that she does. The other two are really irritated by it though and are starting to talk about her doing it when she leaves the room- they are saying that it's weird and that they find it a bit grim. I'm worried that she might overhear at some point and also that it might start to show with them that they're annoyed about it. I was just wondering if anyone else has had a similar situation (not necessarily sucking their thumb but another habit that has annoyed others) and if so, was there anything that they could do or that helped the situation? thank you

It's not really doing anyone any harm. Just mind your own business, maybe it gives her comfort

It's typical, even "normal", for many adults to have a negative reaction when viewing or even learning about an adult who sucks their thumb. Though she isn't interfering with anyone else's legal rights, the noises she makes can be considered an unfair intrustion.
If they understood, however, that the habit is far more widespread, at least in the United States and England, than otherwise known with reasonable estimates of from 3% to 7% of the adult population under the age of 37 (and one estimate has it as high as 10%! I doubt that figure, though it's possible) it may undermine any automatic reactions to the discovery.
I propose the following ideas:
Can she control the noise? Can she be placed in an area that is walled off from the main office? Can a sound machine emitting white noise mask the sucking sounds? How about music playing quietly in the background?