  Low-temperature electron magnetotransport in single GaAs quantum wells with
two populated subbands is studied at large filling factors.
Magneto-inter-subband (MIS) and acoustic-phonon induced oscillations of the
dissipative resistance are found to be coexisting but interfering substantially
with each other. The experiments show that amplitude of the MIS-oscillations
enhances significantly by phonons, indicating "constructive interference"
between the phonon scattering and the intersubband electron transitions.
Temperature damping of the quantum oscillations is found to be related to
broadening of Landau levels caused by considerable electron-electron
scattering.
