  We investigate the frequency and amplitude of the millihertz quasi-periodic
oscillations (mHz QPOs) in the neutron-star low-mass X-ray binary (NS LMXB) 4U
1636-53 using Rossi X-ray Timing Explorer observations. We find that no mHz
QPOs appear when the source is in the hard spectral state. We also find that
there is no significant correlation between the frequency and the fractional
rms amplitude of the mHz QPOs. Notwithstanding, for the first time, we find
that the absolute RMS amplitude of the mHz QPOs is insensitive to the parameter
Sa, which measures the position of the source in the colour-colour diagram and
is usually assumed to be an increasing function of mass accretion rate. This
finding indicates that the transition from marginally stable burning to stable
burning or unstable burning could happen very rapidly since, before the
transition, the mHz QPOs do not gradually decay as the rate further changes.
