Have you tried contacting VZW about this? Not trying to run you off, but with 70 something views on this post, looks like people don't have an answer or don't have the same problem.
My bionic does the same thing but it doesn't happen all the time so I haven't taken it in yet. It seems like loud noises and deeper voices cause it to happen.
I had a D1 that did the same thing I just exchanged it. I just hate that it doesn't do it all the time. I don't want to take it back into verizon and it doesn't do it. But I just got mine last friday and paid to much for a defective phone so Im just going to hope it does it when I show it to them.