The 5e rules say if you are unnoticed you can attempt to remain unnoticed. If you are currently being noticed, on the other hand, circumstances are inappropriate for you to attempt to hide. You need to do something to escape notice first, like stay quiet and out of sight.
You're mixing up 'noticed'. You are making 'un-noticed' = 'un-observed', but rules-wise 'un-noticed' = 'hidden'.
You have to be un-observed in order to
attempt to hide (whether there are current witnesses or not). But before you successfully hide then, although 'un-observed' you are
not 'un-noticed', because you can be heard, signs of your presence are un-concealed from senses other than sight. JC talks about bumping into things, creatures being aware that an invisible creature has struck them, and so on.
In the situation we're discussing, the rogue is in combat with the enemy. The enemy can see him. The rogue is currently being observed. He is not hidden.
The rogue wants to hide. He will have to take the Hide Action In Combat (because being in combat means he needs to take actions to do stuff), but he is not allowed to take the Hide action while he is being observed.
So the rogue has to do something to become un-observed. Note that being 'un-observed' is
not the same thing as 'un-noticed' in 5E. The rogue can become invisible if he has the means, or he could move behind the big packing crate in the middle of the warehouse floor, which takes him out of the direct line of sight of his enemies.
Now he is 'un-observed', but
not yet 'un-noticed'. The enemy watched him move behind the crate, they know he is there, they can hear his feet scuff the floor, hear his weapons and armour creak in their harnesses, whatever fluff reason you want to use to explain that he is not yet hidden.
The rogue's un-observed but un-hidden status still provides meaningful benefits: the benefits of being invisible with regards to his enemy, at least until they or he moves back into line of sight. But he is not 'hidden'. He is still 'noticed'.
If he wants to become 'hidden' (and 'un-noticed') then while he remains un-observed he must take the Hide Action In Combat. He needs to make a Stealth check, and this single check is opposed by each enemy separately; he becomes hidden with regard to those enemies whose Perception check he beat but remains un-hidden to those whose Perception checks exceeded his Stealth.
The crucial part here is
at the moment these contests are rolled that the rogue is
trying to
change from being 'un-hidden' to 'hidden'. Therefore, any tie means that his situation remains unchanged regarding that enemy; he remains 'un-hidden'. In this scenario, the tie effectively goes to Perception.
This would not be the case if the rogue was already hidden when the enemy started looking for him. Imagine the rogue runs into the warehouse a few seconds before the enemy and moves behind the crates and takes the Hide action. He rolls a Stealth check.
Then, when the enemy run into the warehouse and look for the rogue, they must take the Search action and make Perception checks. Those whose checks beat the rogue's Stealth 'notice' his presence even if he remains out of their line of sight. Those who fail to match the Stealth roll do not notice him; he is 'hidden' with regard to them.
But if the Perception roll ties with the Stealth roll, as always the situation remains unchanged. In this case the rogue is 'hidden' when the enemy enter the warehouse, so he remains hidden on a tie. In this case, the tie effectively goes to Stealth.
In regard to JC's comments, when using 'natural language' we all tend to talk about 'who beats who'. We rarely talk about ties because it's a mouthful to say "equals or exceeds" every single time. JC wasn't commenting on what to do in a tie.
