Summary form only given, as follows. Microwave tubes have been plagued by what has been called 'ion noise' for decades now. This is a slow phase modulation of the output signal in time with a period that typically depends on the background pressure. Recently there has been an extensive study of the ion noise phenomena at NSWC, Crane, Indiana on a CW X-band tube called the continuous wave illuminator (CWI). These measurements attempt to ascertain properties of the ion noise with microwave measurements. Earlier, there had been an analogous study of ion effects in a high power klystron, this time by studying the ion current to the cathode. These measurements are in many ways complementary. This work discusses initial theoretical interpretations of these measurements. Some things analyzed are the effect of the beam ripples and ions on the microwave phase shift, the effect of ionization by the secondary electrons, steady state ion current to the cathode in a beam with no ripples, ion relaxation oscillations in a beam with ripples, and the effect of a depressed collector and its role as a Penning trap for the secondary electrons. Finally, the possible role of different types of particle in cell numerical simulations is discussed.