  We consider universal quantization with side information for Gaussian
observations, where the side information is a noisy version of the sender's
observation with an unknown noise variance. We propose a universally rate
optimal and practical quantization scheme for all values of unknown noise
variance. Our scheme is interactive, uses Polar lattices from prior work, and
proceeds by checking in each round if a reliable estimate has been formed. In
particular, our scheme is based on a structural decomposition of the underlying
auxiliaries so that even when recovery fails in a round, the parties agree on a
common "reference point" that is closer than the previous one.
