Three nights ago we were on a slip at leverick. Every 10-20 minutes we heard something like the boat hitting the dock, or someone hitting my rigging with a rubber mallet. This went one all night long. In the morning we found every one else heard the same. Only explanation I could muster is they were blasting a channel.

Mosquito Island construction perhaps?
G

Any chance there was a megayacht in the area? Some of them employ underwater defensive sonar mechanisms that can detect divers, etc. under the boat. The "ping" from them can sound like a bang or loud click, depending on how close you are to the source.

Highly unlikely. Most of those security systems are passive listening for divers inhaling and exhaling and other sounds found outside of nature. Some do have active sonar "pinging". A ping every 10 or 20 minutes would provide little security value.

A dull thud sound was likely another boat or item in the water banging into the dock or boat. Next time you are in a pool bang something on the bottom and see how that sound travels in the water. A big plastic hull would certainly pick up that sound. Even a rudder flopping around can make a lot of noise.

At our marina in Ohio, we hear sounds you are describing during spawning season for carp and other fish. The females bang against the boat bottoms as they are releasing eggs. Is it season for any fish in the BVI right now?

LOL....
That last line.....
all in good fun.......