  Ultrasound velocity measurements of the orbital-degenerate frustrated spinel
MgV$_2$O$_4$ are performed in the high-purity single crystal which exhibits
successive structural and antiferromagnetic phase transitions, and in the
disorder-introduced single crystal which exhibits spin-glass-like behavior. The
measurements reveal that two-types of unusual temperature dependence of the
elastic moduli coexist in the cubic paramagnetic phase, which are resolved by
magnetic-field and disorder sensitivities: huge Curie-type softening with
decreasing temperature, and concave temperature dependence with a
characteristic minimum. These elastic anomalies suggest the coupling of lattice
to coexisting orbital fluctuations and orbital-spin-coupled excitations.
