I think you're probably hearing a gritty chain and nothing else, since it only sounds that way when the chain is running.

It sounds like you degreased the chain too thoroughly, and either washed some grit up onto the inner side of the plates on into the chain, or washed all the lube out. If your chain has a reusable master link, remove and wash it thoroughly in either solvent in a coffee can, or in detergent and water in a soda bottle, and rinse and repeat until the liquid stays clean. Dry it completely (if you water washed bake it dry at 200 for 10 minutes or so), or for solvents give it time in a warm ventilated place (put it on a rag in your car parked in the sun for a while).

Also make sure your sprockets are grit free, use the edge of a stretched rag show shine style on each cassette sprocket.

Re lube and re-mount the chain and you should be fine.

If you want a short cut, cut a paper towel into strips and feed them into the gap as the chain winds onto each sprocket one at a time and run it around that way for a few pedal revolutions. This does a decent job cleaning grit from the inside of the plates and sides of the sprocket teeth. Re-lube the chain and wipe off the excess, and see if that cures it.

BTW- I don't think this is your problem but the two end nuts of your axle should be tight so that neither can turn with respect to the axle or to each other. If either can turn, there's a good chance that your hub bearings won't stay adjusted, and that needs to be corrected. I don't think it's the source of the noise because it would be the same if the wheel were spinning whether you were pedaling or not, but don't let it go.