Not sure if both or one of my rear wheel bearings are failing. Can anyone set me right?

start first with describing the sound that you are hearing, then mabye you can help

Sorry, too little too late. I couldn't wait any longer. Besides, sorry if it sounds crass, but asking for a sound after I already asked for a sound is like, no, it IS answering a question with a question! Anyway, I pulled both hubs off. One spun very loose with a 'flat spot' somewhere on the bearings. The other was still OK, but wasn't far behind the one that failed. for the record, the sound I wasn't sure of was that of two round metalic objects rolling in contact under great load, WITH a soft and barely feel-able thump-thump with wheel rotation.