  Timing analysis provides information about the dynamics of matter accreting
on to neutron stars and black holes, and hence is crucial for studying the
physics of the accretion flow around these objects. It is difficult, however,
to associate the different variability components with each of the spectral
components of the accretion flow. We apply several new methods to two Rossi
X-ray Timing Explorer observations of the black hole binary GRS 1915+105 during
its heartbeat state to explore the origin of the X-ray variability and the
interactions of the accretion-flow components. We offer a promising window into
the disc--corona interaction through analysing the formation regions of the
disc aperiodic variabilities with different time-scales via comparing the
corresponding transition energies of the amplitude-ratio spectra. In a previous
paper, we analysed the Fourier power density as a function of energy and
frequency to study the origin of the aperiodic variability, and combined that
analysis with the phase lag as a function of frequency to derive a picture of
the disc--corona interaction in this source. We here, for the first time,
investigate the phase lag as a function of energy and frequency, and display
some interesting details of the disc--corona interaction. Besides, the results
from the shape of amplitude-ratio spectrum and from several other aspects
suggest that the quasi-periodic oscillation originates from the corona.
