  The Cadmium Zinc Telluride (CZT) Imager onboard AstroSat, consists of
pixelated CZT detectors, which are sensitive to hard X-rays above 20 keV. The
individual pixels are triggered by ionising events occurring in them, and the
detectors operate in a self-triggered mode, recording each event separately
with information about its time of incidence, detector co-ordinates, and
channel that scales with the amount of ionisation. The detectors are sensitive
not only to photons from astrophysical sources of interest, but also prone to a
number of other events like background X-rays, cosmic rays, and noise in
detectors or the electronics. In this work a detailed analysis of the effect of
cosmic rays on the detectors is made and it is found that cosmic rays can
trigger multiple events which are closely packed in time (called 'bunches').
Higher energy cosmic rays, however, can also generate delayed emissions, a
signature previously seen in the PICsIT detector on-board INTEGRAL. An
algorithm to automatically detect them based on their spatial clustering
properties is presented. Residual noise events are examined using examples of
Gamma Ray Bursts as target sources.
