While fighting through a wizard's tower, the party breaks into an unexplored storeroom to take cover from enemies down the corridor outside the room. Unbeknownst to them, there is an invisible skeleton standing against the far wall of the room with instructions to attack anyone who walks within 5 feet of its position. Due to the ongoing fight, the room is also subject to the effects of a silence spell, which will likely end in a round or two when the party shoots the mage maintaining the effect.
The problem is that the skeleton in the room has not taken the hide action, and thus is not hidden (this is because it is exploiting flaws in the command it was given to try and get its master killed), and thus I need to describe the situation in such a manner that the players are aware of what general space the creature occupies so that they can make their attacks with disadvantage against it if they want. It also seems like I need to give them some information about what it is because otherwise several of the party members will be unable to tell the invisible silent unhidden skeleton apart from the invisible silent intermittently unhidden party rogue, which seems contrary to the idea that people aren't allowed to be confused about what space you are in or what's in a space unless you take the hide action (see, e.g., Do you need to take the Hide action when you are Invisible, make no noise and leave no traces?).
As a result, I'm unsure how to provide appropriate description. The skeleton doesn't smell particularly of anything (and the party barbarian is currently coated in excrement from a wrestling match with an Otyugh in the basement), no one is touching it currently and it's not moving, there's no sound in the room and if there were the party nonetheless couldn't hear it, and furthermore they can't see the skeleton.
I've considered using slight temperature variations in the future to handle this (e.g. "you feel an almost imperceptible chill emanating from the middle space along the back wall as you enter this room"), but that relies on the creature altering the temperature around itself and while that works for ghosts it doesn't really fit with the way I've been running skeletons so far.
How can I best narrate the information I need to communicate here?