The answering machine is making noise and there is a photovoltaic system connected to the house. What can cause this?
First, you need to verify that the two things are related. A bad phone line can make a noise with no PV system. If the noise is only with the answering system, it could be a defective answering system that would make noise regardless of the PV system. Seeing two things and associating them without determining an actual link can lead to a lot of wasted time debugging things that are not bugs.
Then, you need to observe and report how they are related (noise when the sun shines = MPPT controller - noise all the time = inverter - likewise, noise should stop when you shut those items down even if the sun is shining, etc.)
The cure will probably be adding capacitors and/or inductors to filter the noise, but without isolating what makes the noise, that's a bit hard to speculate further on. For noise on 120/240V power, a surge capacitor (UL listed, of course) also has the handy function of reducing EMI (electromagnetic interference - or noise on your phone line, in this case.) But if the noise is really from a MPPT charge controller, a surge capacitor on the AC side of things won't help much.
It's also worth checking and rechecking all the grounds - both that they are there, and that they are well-connected.