Sometimes oxidation on the inside of the stem can have a very strange aroma, like mold mixed with tractor grease. I have had a new pipe that had been in storage for a long while that had this issue. I took it into the Briary and he put one end of a churchwarden pipecleaner into a vice and dipped it into pipe sweetener, and worked the stem on the pipecleaner back and forth for quite a while, rotating it frequently. It went away... for a while, and then returned. I eventually just tossed the pipe. It was beyond being able to tolerate.
Learn some, lose some.
Learn some, lose some.