They tested one off of LA a while back.
There is no proof of that. Every ocean in the world is monitored by the SOSUS network.The SOund SUrveillance System (SOSUS) provides deep-water long-range detection capability. SOSUS enjoyed tremendous success during the Cold War tracking submarines by their faint acoustic signals. SOSUS consists of high-gain long fixed arrays in the deep ocean basins. The U.S. Navy would have picked it up.