You will be able to determine "bad spindle bearings" after you get the pulleys drive belt off.
Using a blade tip as a handle, push "up and down" on the blade ("toward and away from" the deck shell).
A worn or "gone" bearing will allow the blade to move quite a bit.
You also can give each blade a spin by hand and listen/feel for a rumble or grinding noise. You may have to defeat the blade brake on one spindle to get it to spin.
Bearings can be found without buying the entire mandrel assembly by visiting a bearing distributor. But if the mandrel casting has been "wallowed out" by a faulty bearing then you will need the complete mandrel assy.
Expect at least some of the bolts that hold the mandrels in place to break off. If your existing mandrels are worth putting bearings in and you break off a bolt..........get back to us with pictures of your mandrel and we can advise on how to deal with that.

So the steps i should do tonight are.

1) Remove belt
2) Check for vertical blade movement
3) Check rotation of both for unexpected noise

If 2 & 3 result in no vertical movement, and no odd noise, what else could explain the noise i've recently started hearing?

I watched a video and now realize the "pulleys" on top of the mandrels have no bearings....but there are two more that do?

Thank you for your help.

If you know the Sears 917.xxxxxx number, you could likely download the Owners Manual for correct belt routing, part #'s etc.
Or go to searspartsdirect.com

OOPS! Looks like I missed the link you posted-

This post was edited by bill_kapaun on Tue, Sep 10, 13 at 14:24

The mandrel pulleys themselves do not hold the bearings. The pulleys fasten to the spindle shaft. The spindle bearings are inside the mandrel casting which is below the pulleys.
There are 2 idler pulleys (items 36 & 145) that have bearings in them also. I believe these are the pulleys you cite above. You can test the bearings in them by spinning each idler pulley and feeling/listening for noise.

Sweet, looks like i might have some difficulty getting this rusty deck apart tonight. I'll post some pictures tomorrow of everything so i can get some opinions as the whether it is worth saving/fixing.

So here is where I stand. I've got pictures and video to post tomorrow.

On blade makes funny noise when spun. Other blade and two pulleys sound okay.

Deck seems solid however it's rusted pretty good.

Blades have no vertical movement.

Probably need new brake pads.

Probably need new spindles.

Got plastic shroud off.

Broke of one bolt of spindle that makes funny noise.

That's where I stopped.

I follow up in the morning.

Okay so i dropped the deck last night, at least that was easy.

Not as clean as i thought it was....

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Here is me spinning the various pulleys

Here is a link that might be useful: Short video of pulley's spinning

Both idler pulleys have worn out bearings, especially so on the second (in order of presentation) idler.
First spindle bearing is showing some noise but should otherwise be acceptable to replace just the bearings in that one.
Second spindle.............hoo boy!
You might get lucky and find that the bearings have simply failed between the 2 bearing races and that the spindle shaft and mandrel casting are still serviceable, but with all the thrashing I heard on that one.................prepare yourself to replace that mandrel as an assembly.
It could have spun the bearing in the case, or on the spindle shaft enough to render either or both........useless.
From all I saw/heard I sum up that your "noise" is not one instrument but more like a 4-piece band.

So I broke all six mandrel bolts off. I'm not gonna mess with trying to rebuild them. The other pulleys bearings are obviously shot when you hold them in your hand and spin them. So two new Mandrels and two other pulleys and it should be okay for a couple more seasons before a new deck is needed. There is one crack And some pinholes rested through where grass exits, but nowhere near where anything bolts to deck.

The grass build up on the top of the deck is because it has air induction, so the clippings get sucked up through the slots in the spindle assembly. That's just how these work and my 2013 yt-4000 does the same thing. I just blow the grass out after each mow.

After you get the deck cleaned up, you could coat it with that black truck bed liner stuff. that would hide any rust scale that was left behind and give a textured look to the deck.

So I made an electrolysis tank, and soaked the deck for a couple of days, with all the rust gone this is what i'm dealing with....

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Well see if JB Weld Steel Stick works...

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Primed and ready for some spray paint tonight....

It is gratifying to see folks willing to work at projects like this.
I realize that there are times when the damage/deterioration is simply too far gone to deal with, but this is a definitely worthwhile task for someone willing to put forth some elbow grease.
I too am of the genera that want to squeeze the "buffalo" on that nickel until he ....well......you may have heard that one if you are old enough.
This type of salvage/repair/restoration is not for everyone and is certainly not the kind of repair you would seek out a professional shop for. But for an able/capable do-it-yourselfer....this is right on the mark.

Thanks for the kind words, and as you pointed out it really all depends on the money.....i was shocked at how well the electrolysis worked. Large pieces of metal, that i thought was solid and wouldn't budge with a screwdriver, fell right off after several hours. You can see the "pits" left over from rust that had "grown" and was solidly attached, giving the false impression of strength/structure. I've got several tools soaking in the tank right now, should be able to fix them up tonight.

I realize the deck may not be perfectly safe, meaning if I hit a rock or something it could come flying through a weak part. The area around where the spindle housing bolts is solid, as is most everything (except where you see all the holes).

At the very least i learned about electrolysis in undertaking/researching this little repair.

Should be mowing in a few days, paint it tonight, maybe get it back together tomorrow we will see.