I make noise when I sneak, unless I have the silence perk or 100% muffle, and the noise I make goes up when I wear heavier armor. Daedric armor with 50% muffle makes more noise than elven armor with no muffle at all.

I understand that the Unhindered and Conditioning perks cause my worn armor to become weightless for encumbrance purposes (and also for moving in real-time; dodging, sprinting, etc.), but does it also cause worn armor to be weightless for noise-while-sneaking purposes?

And what about the Steed Stone?

I can't confirm that. I would be slightly taken aback if it did. I find the idea of specializing in heavy armor for the sake of stealth to be slightly amusing.

How about just wearing what you find suits your character?

I believe it does affect sneaking as well although I'm not certain. I'm pretty certain on my original playthrough I found it much easier to sneak (even though I barely ever snuck anywhere) up on enemies when I'd taken that perk, even though my sneak skill was really low and I was dressed entirely in ebony armor (minus helmet).

I just go with fur armor it looks good for a nord

Conditioning/Unhindered make it so the armor doesn't slow you down when worn. Meaning you wont waste as much stamina when you sprint. Whether this has an effect on sneaking or not, im not sure. Im currently 76 in sneak at lvl 33, so the fact that heavy armor is noisy is basically negligible with the perks I have. The perk does make armor weightless, but only when worn. The armors weight doesn't magically hit zero

Isn't there a sneak perk that allows all armor to cause no extra noise while sneaking? I think there is because I can sneak right next to someone in full heavy Ebony armor and go unnoticed.

it cuts noise by 50%, actually. Its called muffled movement. So, your armor will still make noise. I recommend wearing either the ebony mail or boots with muffle enchantments

Ah, very good. I knew there was something of that sort. Just thought it cut noise altogether.

I believe the Nightingale Boots muffle all movement making their wearer completely silent.

just take off your armour if you are so intent on being perfectly silent (nothign like sneakin' around in your birthday suit, eh )