Noise (hissing / water fountain) on incoming main water line

About 2 days ago, I started hearing some hissing / water fountain (falling water) type noise coming from the main water line that is entering my house. The noise was pretty loud.

Here is video showing the noise: https://drive.google.com/file/d/1vDaFcgrHYO4sZ1LAMlY2_SU2GbxThxU6/view?usp=sharing


1. I turned off the water coming into the house by turning the valve on the main line.

2. I drained all the water from the internal plumbing by turn on the kitchen sink, and the exterior faucet (shown in video)

3. I checked all the sinks/toilets in the house and there are no leaks of any kind and/or any sound coming from the interior plumbing. The house was built 2.5 years ago so it is fairly new.

4. Then I turned the water line back on. The noise has died down considerably but I'm still hearing a hissing / drinking from a straw kind of noise if I stand nearby.



4. I also dug up a little of the mulch around the main water line but the ground isn't wet. So I am not sure if there is a leak somewhere near the main line (in the underground pipe) or some debris is stuck or what the source of this noise is.

6. I will call my plumbing company tomorrow and see if they can come out and inspect it and advise as to what is going on. I have plumbing maintenance as part of my annual contract with them so I'm hoping they'll check this out and advise on what is going on.

Based on the video, what do you guys think?