  We investigate the origin of the ubiquitous 0.5 - 10 Hz QPO in the Galactic
microquasar GRS 1915+105. Using the archival X-ray data from RXTE, we make a
wide band X-ray spectral fitting to the source during a low-hard state observed
in 1999 June. We resolve the X-ray spectra into three components, namely a
multi-color disk component, a Comptonised component and a power-law at higher
energies. This spectral description is favored compared to other normally used
spectra like a cut-off power law, hard components with reflection etc. We find
that the 0.5 - 10 Hz QPO is predominantly due to variations in the Comptonised
component. We use this result to constrain the location of the various spectral
components in the source.
