Localized oscillations present in the crystalline phases of the heneicosanoic acid Langmuir monolayer were studied in detail. They appear like blinking interference rings, when observed with Brewster angle microscopy. Monolayers with localized oscillations were transferred on mica to be characterized by atomic force microscopy. We found granules produced by the expulsion of matter from the monolayer. However, these granules are too short to produce Newton's rings; the common belief of the origin of the interference rings in the field of Langmuir monolayers. The analysis of the light intensity distribution and the sizes of the rings are consistent with Airy patterns produced by Fraunhofer diffraction due to the reflected light from the multilayer granules. The origin of the blinking of these patterns is still unclear.