  We report magneto-acoustic quantum oscillations (MAQO) in the heavy fermion
system UPt$_3$ in magnetic fields B, upto 33 T. For B in the ab-plane of the
hexagonal crystal MAQO in the sound velocity commence at $\approx$ 12 T and
grow with field. However, in contrast to typical Lifshitz-Kosevich behaviour
the frequency corresponding to the dominant oscillation increases continuously
as the metamagnetic transition (MMT) at 20 T is reached. This dominant MAQO
arises from the $\delta$ orbit of band 1 with a large effective mass of 33
m$_e$, for B $<$ 20 T and disappears after the MMT. Thus, the MMT involves a
significant change of the Fermi surface, primarily in band 1. For B $\parallel$
ab-plane and $<$ 20 T we reproduce successfully orbits established through
previous de Haas-van Alphen and Shubnikov de Haas measurements. We also observe
several new orbits, some that can be identified with existing band theory and
others not seen previously with completely new frequencies. For B $\parallel$
c-axis we observe MAQOs which also commence at $\approx$ 12 T and grow
gradually but break suddenly into a large amplitude and change in frequency at
24.8 T. These enhanced oscillations get weaker again at 30 T. These abrupt
changes at 24.8 T and 30 T are signatures of Lifshitz transitions and coincide
with the newly discovered spin density wave states for this orientation
reported by us recently.
