I know when I was with Sprint they sent me a Airave unit because the signal at my house went from great to non existant in 6 months. When I would push the connect button to receive a call or place one I would hear three fast beeps. Sprint says it is to tell you that the call is going through the Airave unit. Are you using any of those devices that let you make calls over the internet? What about people living around you in other apartments or condo's or even houses for that matter.
Should have asked this first, does this only at your home or all the time no matter where you are at? If the later is true forget what I said above and call Verizon.