That wasn't what I expected to hear, to be honest. Normally people say 'noise', and we get horrible digital bus noises and computer generated rubbish - yours is good old fashioned hiss. Nothing there to filter out as it's wide band, so as we're hearing hiss not hums, you n' do much with it, other than try to work out the problem. The no guitar sample - recorded with simply the guitar unplugged? As you have tried different PCs and different interfaces it's got me confused a bit. What could cause wideband hiss. Normally we'd blame the interface, but if you have swapped this lot, with identical noise then the only thing left, now we're removed the interface and computer is the guitar? Have you swapped that too, just to remove it from the scan trio you have? My guess was going to be a low output from the guitar, which means the gain has to be cranked up, bringing with it the noise. All preamps hiss to a degree, but the wanted vs unwanted signal usually means the hiss is far enough down to be lost - especially when guitar processors are used, which are themselves inherently noisy because of how they need to boost to distort. I guess we can start to experiment. Plug in a shorted jack plug, which silences the input. Any hiss you hear is then being generated inside the interface. In my systems, the interface takes total control of the input gain - you've n to set yours up oddly, so the interface is being padded by some weird setting you have applied to the computer audio system. I cannot make my system do it, but if your interface gain has to turn up high, it will produce this hiss. Maybe the interface gain is too high because your computer gain is somehow turned down? I can't do this on mine, but maybe something you do is turning it down? Last thing is simply the guitar - could it be very low output? Doubtful. I assume it works fine into an amp. The last guess is the clue with the DI. You are going into the DI box, and then connecting the XLR out to the mic input? DI boxes sniff an instrument level input and then drop this down to mic level, which then has to be boosted back up? The UR22 has a socket for a guitar - does this have more or less noise than the mic input? How far is the gain control rotated too?. If it's ¾ or more then the hiss is going to be there. Your sample files show us hiss - but we have no idea how far that is below maximum? If you plug an MP3 player, CD player or anything similar into the interface and turn the gain down to give a realistic level is that hissing too? Or does turning down the gain, turn down the hiss.

I hear no interference, hums or impulse noise that filters and conditioners might have sorted - just plain old fashioned broadband hiss. Do microphones have the same hiss?

it sounds to me like hiss from whatever you are using to get high gain from your guitar. try turning that off and playing the guitar clean to see what happens. most distortion pedals make that exact noise. so will any high gain modeling amp sim plug or emulation. the only answer is some noise gates and a guitar with pups that have higher output. even with louder pups it's still going to be there a bit. signal masks noise.

Just a guess, sometimes weak or over taxed (guitar effect) power supplies or low batteries can cause hiss.

Are we assuming that his connection order is guitar - processor - audio interface? If so all he has to do is remove the input from the interface and see if the noise stops.

Where does the OP mention a processor or a pedal between the guitar and the interface? Is it because the recorded sound is so distorted, or did I miss something else? We also do not know whether he/she (not easy to tell from that name) is connecting via a DI box into a microphone input or into a hi-Z input on the interface.

I have been presented with hissy guitar outputs in my time, and I generally start by assuming that the guitar has built-in electronics struggling to run from a flat battery. However, the OP states that several guitars have been tried and they all produce the noise.

op said thaty were direct into the interface. i am assuming there is some kind of overdrive gain sim or plug going on because it is so distorted. how else can distortion like that be generated? increasing gain is the only way i know. i don't understand the resistance. just turn off the distortion and see what it sounds like.

op indicates the noise happens even when a guitar is not plugged in. to me that says there is a high gain amp, sim or something going on.

Yep - we're all guessing, but he's doing something odd as those interfaces are not the quietest, but perfectly usable. Maybe he has an insert effect semi-permanently applied if he always records that kind of guitar sound? I guess we have two wait for an explanation.

I know guitar pickups don't have the same output level.. What the OP may need is an external active Di..
Like this : http://www.radialeng.com/product/pro48/
or a J48

or higher gain pups.

I have another idea !! The thing with the entry level audio interfaces is that when you crank the volume pass 70% they are usually noisy. That's why I suggested an external DI
But a thing that you must check is if the input chosen is switched to di / instrument. Most of those inputs are combos XLR/TRS and you need to go to the drivers or the realtime mixer to switch the input between mic / line / instrument...