Can You Dig It?

My office is in the basement of my house. As might also be expected, the main water line comes into our basement. This means that I know when someone is using a toilet or sink upstairs because I can hear the water flowing through the pipe. For the past week or so I've heard a steady hissing coming from the water pipes. At first I thought maybe we had a leaking toilet or faucet, but I couldn't find one. That's when I got nervous and went into serious troubleshooting mode.

When I turn off the house's main shut-off I can still hear the noise. When I turn the water off at the street I don't hear it anymore. This tells me that the problem is somewhere in the main supply line. I hope that being able to hear it means that the leak is near the house.

I spoke to a general contractor that we've used before and told him my thoughts. He thinks my diagnosis makes sense. He also told me that the supply line is likely PVC. If that's the case I think I can fix this myself. I am really looking forward to stopping work for the day so I can dig up my yard and see what is going on with this. I really want an end to this literal drain of money.