I've experienced the same. I find the idea of 'getting on the sound' to be very helpful. My understanding is that the premise of why we block in those situations is a fear of stuttering. So, consciously or subconsciously, we dont let any sound out at all due to the fear of it being a stutter. Getting some sound in to that block has helped me be brave in getting the sound moving and not hearing the stutter. Take a look at Vivian Sisskin's work on this - she's got a bunch of material on YouTube and explains it much better than I can.