An old bike of mine had a creak that I thought was coming from my pedals. Turns out it was coming from my rear wheel hub. I took apart the rear wheel assembly, cleaned out the cup, cone and balls, greased and reassembled. It appeared that the hub had gotten too tight. The creak was gone, but now its coming back. What would cause a wheel hub to go out of adjustment? Could it be the derailleur? The rear derailleur doesn't have an adapter, its just bolted onto the rear axle--it came that way. It has worked and while I've been meaning to get the part, it hasn't been a priority. Meanwhile, it shifts okay.

There's really no easy way to tell for sure what's wrong in this format. You need to securely tighten the locknuts on both sides against the cones, and they should have a washer between them. It's also possible there is pitting/wear on the bearing surfaces. New grease and ball bearings will not fix a bad surface.

True enough, but I didn't see any red flags and post service it was feeling nice. Also the creak came back slowly, as if pedaling was aggravating the problem.

the only way i could think a hub could "creak" would be if the axle or the hub was cracked.

if your hub keeps tightening itself, i would check to make sure it's not rubbing somehow on your dropouts.

A few possibilities come to mind. It's possible that your dropouts aren't parallel, which is common on older bikes. That will bow the axle slightly when it's tightened effectively shortening it and tightening the bearings. Try re-adjusting, but leaving it a hair loose and see if it comes to a perfect adjustment when in the frame.

Pedaling can aggravate a bearing problem, especially on hills. The load from chain tension is greater than the load from axle weight, and might push a borderline situation over the edge.

In my experience ball bearings don't tend to make a creaking sound. Look at the hub carefully ans see if a seal or dust cover might be touching the axle. If you have a reason to open it, you'll see polished or scored areas on one side of a cone.

Lastly, your axle mounted RD wouldn't affect anything if, as cny-bikeman suggested, the locknuts on both sides are properly tightened.

Most don't recommend re-using existing ball bearings; once you have the hub apart toss 'em and buy a new set. They're cheap. Getting the adjustment just right is as much art as science....

But I agree; I've never heard any sort of "creaking' from even a totally lunched hub. Sounds like an old coffee grinder if anything. Usually, creaking is some sort of metal-to-metal contact.

If the balls are clean and shiny they can be reused.
The adjustment on a hollow quick release should be a little loose so that when the QR is closed it compresses the axle making the final bearing adjustment.
If you removed the right cone be sure that you get it very tight. If you don't it will move against the cone and eventually ruin the hub.

If anything in a wheel hub is going to creak I would expect to be either the spokes or the quick release skewer. Assuming the spokes are all equally tight then I'd suggest lubing the quick release joints and camming surfaces, which are internal in the Shimano skewers, and see if that makes it go away.

And if that doesn't make the creak go away then look farther afield. I once had a squeak or creak that I SWORE was coming from my pedals. It even responded to loading the crank arms by standing and pounding on the arm. So I figured either crank to BB joint or the pedal. Turned out to be the seat post to frame was getting too "dry" from a couple or three years of wet weather commuting. Cleaned and greased the seat tube and post and it was silent as a stone. So the sounds don't always come from where you think....

I greatly appreciate the assistance and I see a good deal of food for thought. I wouldn't be surprised if the dropout aren't perfectly parallel and I will be checking them. The notion that something may be rubbing against something else also makes sense. When I have the bike upside down and spin the rear wheel, I notice a slight but definite wobble where the freewheel is, so there could be rubbing. I don't know what it indicates. The bike has no quick release. I don't think its not particularly valuable. Its kind of retro (reminds me of when I was growing up and 10-speeds were popular), rides well, it came almost free and I suspect its reparable without much cost.

It's definitely not unheard of for a cone adjustment to loosen up. You just have to recheck every now and then.

Don't go nuts on the locknut torque. That's not the problem. Parts are wearing in.

However, roll your axle across a smooth surface to see if it's not bent a little. It will slowly bend more and more if it is, ruining your adjustment.