Using prosodic information to predict when back-channels are appropriate in spontaneous dialogs has become somewhat of a reference problem for automatic discovery techniques. Here we present experiments with two ideas: the use of features derived from randomly generated pitch and energy filters, and the use of instance-based learning, specifically the Locally Weighted Linear Regression (LWLR) algorithm. For the task of predicting possible back-channel locations in Iraqi Arabic [6], we obtain 22% precision and 51% recall, which is as good as that obtained using a laboriously developed and hand-tuned rule.