  The evolution of extragalactic radio sources has been a fundamental problem
in the study of active galactic nuclei for many years. A standard evolutionary
model has been created based on observations of a wide range of radio sources.
In the general scenario of the evolution, the younger and smaller
Gigahertz-Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources become
large-scale FRI and FRII objects. However, a growing number of observations of
low power radio sources suggests that the model cannot explain all their
properties and there are still some aspects of the evolutionary path that
remain unclear. There are indications, that some sources may be short-lived
objects on timescales of $10^4$ - $10^5$ years. Those objects represent a new
population of active galaxies. Here, we present the discovery of several radio
transient sources on timescales of 5-20 years, largely associated with renewed
AGN (Active Galactic Nucleus) activity. These changing-look AGNs possibly
represent behaviour typical for many active galaxies.
