My ferret is making a slow huffing/ like Sighing sound

[Rey]

My ferret bandit has been with me since a baby he’s now 6 and I recently like 2 weeks ago got fefe also an older ferret don’t know her exact age. We thought they were getting along fine but I recently noticed that he goes and looks for her wherever she’s sleeping and just huffs and puffs at her it looks like a sigh I can’t quite tell I’ve looked up all the signs but the best way I can explain is repeated sighs at her. He just lays his head next to her body and sighs repeatedly and he only does it around her. His tail isn’t puffed while doing this and he doesn’t attack her after or before doing this. I’ve listened to his breathing away from her and he is breathing fine no signs of any respiratory trouble. I can’t tell if he’s sad cuz she’s asleep and he wants to play or if he doesn’t like her. I don’t know what to do please help let me know what this could possibly mean

[abbeytheferret6]

I am not familiar with that sound---just hissing although my Didi and I came around a corner once and we both let out a screech.
I would not worry if he does not attack her or anything.

[eclipso]

Here is something I found on an article:

Ferrets can get depressed, just like people. The loss of a cagemate or a human companion can trigger depression. The ferret might search for its companion in places that their missing friend usually occupied. The ferret might slouch down like it is in pain and sigh a lot, but it won’t have the squinty eyes of a ferret in physical pain.

be.chewy.com/ferret-communication/

Maybe your ferret just feels lonely when she's asleep or is sad that she won't play when he's awake. I also found that a lot of people say their ferrets sigh to something that they don't like is happening. When people hold them for too long, the ferrets will sigh. If they say no, the ferrets will sigh too. I don't have a ferret yet, so I'm not that familiar with their behaviors. I hope someone else can help some more.