  We image and characterize the mechanical modes of a 2D drum resonator made of
hBN suspended over a high-stress Si$_3$N$_4$ membrane. Our measurements
demonstrate hybridization between various modes of the hBN resonator and those
of the Si$_3$N$_4$ membrane. The measured resonance frequencies and spatial
profiles of the modes are consistent with finite-element simulations based on
an idealized geometry. Spectra of the thermal motion reveal that, depending on
the degree of hybridization with modes of the heavier and higher-quality-factor
Si$_3$N$_4$ membrane, the quality factors and the motional mass of the hBN drum
modes can be shifted by orders of magnitude. This effect could be exploited to
engineer hybrid drum/membrane modes that combine the low motional mass of 2D
materials with the high quality factor of Si$_3$N$_4$ membranes for
optomechanical or sensing applications.
