Symbiotic pair? Goby + shrimp!

I am really loving my watchman goby! He has completely tunneled out the substrate in my FO tank! I actually lost a frag in his tunnel last night. Slippery piece of sarcophyton slid right down his chute! I am hoping he'll want it out of the way but it could be lost forever! The tunnel structure goes around the entire tank, so he has little exit holes all over. I never know where he is going to pop up! Kinda like that arcade game?

But, I was not sure his buddy shrimp was still in there. I have never seen it since I added this pair last spring. Last night I was playing with my camera and caught this pic:

You should be able to hear him. . . .loud clicking sounds??

I've never heard clicking from him.

My seahorses, though, I can hear their snick from the next tank! I am going to see if we can hear it on video...

When I had my pair I could hear the pistol shrimp click on a regular basis--then the mantis hiding in my tank got him...  
Also, with time the pair came to accept that there were people walking around and wouldn't bolt everytime they saw me, though I had to approach slowly to not have them dart into the hole.  The pistol shrimp continously moved sand around--and used anything he could find for shoring up the walls, including any frags that got knocked over by anything else.