Dynamic spectra of Saturn Kilometric radiation (SKR) obtained by the Voyager planetary radio astronomy experiment have been searched for variations at a time scale longer than that of the arcs (about 1 hour). Two kinds of episodic changes of the shape of the dynamic spectrum can be distinguished: one is an overall long-term change, lasting for one several Saturn rotations: the other is a modification of the dynamic spectrum from one rotation to another limited to the sub-solar longitude range from about 270¿ through 0 to about 60¿. Both correspond to a change in the shape of the intensity spectrum of the emission. The long-term variation probably contains the so-called ''Dione gaps'', together with similar and sometimes much longer events. The already discovered influence of strong solar wind activity corresponds to increases of the average intensity level of the emission, but not to changes in the shape of its intensity spectrum. Both kinds of episodic spectral variations are usually observed in magnetically quiet conditions, in particular when Saturn enters Jupiter's magnetic tail. These changes of the SKR spectrum are compared with those already observed in the terrestial kilometric radiation. They could be due to complex propagation effects, temporary modifications of the emission beam or changes in the source altitude.