What Causes Bad Smell From The Upper Back Part?

Hello Occasionally I have a very strong smell which emanates from my back -primarily my upper back. For the past two days it has been quite strong. I should mention I have very good hygiene and shower every day and twice a day quite often. Yesterday, I could smell it a few minutes after I showered. I went and took another shower using only very hot water figuring it would open my pores. Then I finished with very cold water to close them. I also have a back scrubber which I use every day to which I applied body wash gel, apparently to no avail.
I experienced the same problem today so asked my wife to smell it. She said it's primarily coming from my upper back. I had her cleanse the area with rubbing alcohol to kill any bacteria which may be present. It still seems the odor is lingering. For several years I've had this occur at times and would smell my shirts and thought the sour smell was caused by sweat which was causing the laundry to have a bad smell.
But it now seems as if I am producing the smell, since it is apparent even immediately after I get out of the shower. There is no apparent rash or change in color anywhere on my back. My skin is smooth and not dry or cracked.
I am a 53 year old male in pretty good health. Any ideas? Thank You!