I shared this on my FB page a few days ago.
Suggestions included the Yellow Submarine, Captain Nemo, the Seaview, and either Russian or American submarines---but not Canadian subs, because none of ours work. All these ideas seemed about equally plausible to me. No-one mentioned methane seeps, though. Does methane ping or hum, perhaps? Maybe if it's squeeeeeezing through a little crack, like wind through the stretched neck of a balloon?
Perhaps a new research study is in order.