I repair phone issues for the cable company I work for. We don't use the ATAs (we use EMTAs), but the principal is the same.

The VOIP service is ran through a digital signal (from emta/ata to isp, and so on). Your actual phone wiring is analog, and this is where static will occur.

Now, if the voice is choppy, or one person can't hear the other, then it could be an internet issue, etc.

With that said, let me ask this: is your entire house wiring hooked into the ata? If so, disconnect that, and plug a phone directly into the ata. See if the static is gone. If it is, you know its your phone wiring. If it's still there, then try another phone, ruling out the possibility of a bad phone. If there's still static, then ata's must operate differently than the EMTAs that I'm used to.

Worth a shot, give it a go