In my 1st Answer, I mentioned a "wired jack" to test in another room. Obviously, no wired jack is needed... I was thinking of a wired telephone (or wireless) to plug into the ST Home Phone box... in any room or location.
You don't even need power if you've got the battery in the box.
I'm really not sure, but sometimes I hear an echo of my voice on mine, which I also sometimes heard with the straight talk cell phone I had.
I can't tell if that is coming from the service or the phones, but it could very well be the service since they are two totally different phones.
Also I don't hear it all of the time, but I noticed it more when standing in some areas of the house versus other areas. So, it may also depend on your service area.
You could buy another phone brand to see if it's actually the phone. Whatever the results, you can either keep it or return it. Hope this helps.
You've probably got some interference in your home. Mine had some weird noises until I changed the channel on my internet router, which was right under the ST Home Phone box. (Best to manually set routers to ch. 1, 6 or 11 rather than "auto" set.) I also put one of my DSL filter in the phone line from my wireless tel. base unit and the ST box.
Could also be other devices nearby... try it in another room, like a bedroom (if you're using a wireless phone with it or you have a wired jack there).
You might have to exchange it if you can't find a source in your home.