I have a VOIP phone on a cable modem and have been experiencing static on my phone. What could be the causes?

At times, there is absolutely no static and the call is fine. Other times the static stays for about 2 secs and repeats often. Could it be the batteries draining out? Could it be an issue with the VOIP equipment? Could it be the wireless phone interfering with something? Or could it be another reason?

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