Mossbauer radiation from a copper foil doped with57Co is resonantly absorbed in a stationary Be∶57Fe absorber. Experiments were performed with the source immersed in liquid He at 4.2K, He gas from 4.2 to 78 K, and in liquid HeII to 2 K. Radio-frequency current pulses through the source cause large increases in transmission, mainly after the end of the pulse. These increases are associated with heat transfer instabilities (Taconis oscillations) at the He-metal interface.