In a previous paper we studied squeezing of mechanical motion for a pa
rticle trapped in oscillating fields. We considered a model proposed b
y Glauber and time-dependent transformations to show that the system m
ay exhibit quantum fluctuations below the shot noise level. Here we pu
rsue this investigation to discuss the regions of instability, where f
or a certain range of parameters, variance of quadrature phase amplitu
des continues to grow with time.