LiNbO-based optical modulators, used for external laser modulation in 10 Gbit systems, were tested at 40 degrees C 95 percent RH under 10 V, 3 V and 0V bias. Environmental conditions, typical of storage tests, were not too different from their operating level, while 10 V bias was roughly 3 times its standard value. Looking for possible leaking paths between the metal electrodes, the parasitic current I was monitored, with a failure criterion I < 1 mA. Within 2 weeks, some specimens under the highest stress reached the failure condition, and other devices, at the end of the test, showed a degradation of the Insertion Loss IL higher than 0.5 dB. Microscopical inspection showed a common feature, namely the occurrence of Au-rich paths, under the typical form of corrosion between the electrodes. Depending on the extension of those paths, a compete electrical bridge was formed, or simply local plating occurred of the inter- electrode surface, which locally affected the electrical properties of that surface. The observed figures are coherent with Au corrosion mechanisms, which has been relevant in environmental test of RF silicon devices many years ago.