Multi-microphone post-filtering allows additional noise reduction at a beamformer output. Existing techniques are either restricted to classical delay-andsum beamformers, or are based on single-channel speech enhancement algorithms that are inefficient at attenuating transient noise. In this paper, we introduce a multimicrophone post-filtering approach, applicable to adaptive beamformer, that differentiates transient noise from speech. The ratio between the transient power at the beamformer primary output and the transient power at the reference noise signals is used for indicating whether a transient is desired or interfering. Based on a Gaussian statistical model and combined with an appropriate spectral enhancement technique, a significantly reduced level of non-stationary noise is achieved without further distorting speech components. Experimental results demonstrate the effectiveness of the proposed method.