This evening when I came home, I heard a "fog horn" like sound. After exploring the various rooms of my house, I realized it was coming from outside. I noticed that my water meter has an attachment, round piece that looks like it has a vent of some sort on it. It appears to be vibrating which explains the noise, but I am wondering what would cause this. The sound / vibration is at intervals of about 30 - 60 seconds and lasts about 5 seconds.

Something that looks similar to this: PRV Watts 3/4 N55BUPEXM1 Water Pressure Reducing Valve

If, so then moving the adjusting screw a little bit might fix it. There is a disk inside that isn't attached to the adjusting screw, so it can move. Probably time to replace it, but first you need to check the house pressure with a hose bib pressure gauge.

Was something running in your house when you heard this sound?
Did the object that was vibrating look like this? (see image) Let me know . Tom

De' Ja' Vue (sp?) Just thought I'd post a image to back you up.

Thanks for both responses. That is not what it looks like. It is more of a round, flat disk. The noise has stopped now. I noticed it just after running my sink and the disposal, but have not been able to replicate it.

Let us know if it returns. What does this disc connect to? Can you take a picture? Cheers, Tom