The I-V characteristics of thin film microbridges containing 90 degree
s basal-plane-faced tilt boundaries (TBs) exhibit pronounced resonant
structure. This structure is attributable to the presence of ''beating
modes'' previously studied in high Q DC SQUID structures having subst
antial shunt capacitance and large inductance. Less pronounced but cle
ar resonant structure is also observable in in-plane c-axis TBs. We di
scuss a model which accounts for this behavior.