I found this on a search for "thermionic noise vacuum tube". This noise could be described as a rushing wind. If you've ever cranked the volume on an old amp you can sometimes hear a hiss in the background. And solid state devices can also exhibit this. Possibly the tubes are heading south. Gradual loss of vacuum displaced by gas may cause the tube to do strange things. I had found some other sites delving into this, but they were ladened with some pretty scary looking calculus to explain the effect !! Not sure if this could be related to a loose socket or not, unless the looseness is interupting connection to one of the elements in the tube.
"Walter Schottky (1886-1976) discovered the random noise due to the irregular arrival of electrons at the anode of thermionic tubes that is called "shot noise" (Schottky effect) in 1914 while studying under Planck in Berlin. Schottky was Swiss, but he was educated and spent his professional career in Germany. In 1919 he invented the first multiple grid vacuum tube, the tetrode. Schottky obtained multiple doctoral degrees, taught at universities from 1920 to 1927, and then worked for Siemans for nearly five decades. He was the first to note the existence of "holes" in the band structure of semiconductors, discovered the type of lattice vacancy known as the Schottky defect, and in 1938 created a theory that explained rectification at a metal/semiconductor interface."
