  Twin kilo-Hertz Quasi-periodic oscillation with ratio 3/2 has been found in
some compact sources, which is believed to be related with their innermost
regions of accretion disks, and hence carrying information of gravity in strong
regime. However, more complicated phenomena have been revealed, e.g., the twin
kilo-Hertz Quasi-periodic oscillation of 4U 1820-20 start increasing at certain
spectral state and then saturate upon reaching certain level. Moreover, such
quasi-periodic oscillation is not uniform and has multiple peaks, which
displays random feature. This letter suggests that these challenges could be
easy to understand if the quasi-periodic oscillation originates in jets of
compact objects. With a seed periodicity originating in either neutron star
spin or accretion, shell collision develops in jet. The corresponding twin
kilo-Hertz quasi-periodic oscillations automatically carry random feature, vary
in frequency; and couple with luminosity, spectral properties, which well
account for the observation of 4U 1820-30. New quasi-periodic oscillation of 4U
1820-30 is predicted, which can test the validity of this model. And the
scenario is applicable to other compact object like AGN.
