Gurgling Conduit

Hi Folks, I've got 240V coming into my detached garage's fuse-box sub-panel from my house's main breaker box. Attachment 42924 (http://www.doityourself.com/forum/attachments/electrical-ac-dc/42924-gurgling-conduit-img_20141115_142514662.jpg) About a week ago, I was checking the six fuses in my garage, because a freezer stopped running, and I was getting ~13V to a few of the fuse sockets, and 120V to the rest. Confused, I reset the "garage" breaker in the house, re-measured, and was getting 120V to the fuse sockets again, so I shrugged it off. I went out in the garage tonight to finish up labeling the fuse-box, and I heard noises coming from its vicinity. After banging around the area with a board to scare away any animal that might be making the noise, the noise continued.