Phone is still ringing for incoming faxes though it is already set to voice only. It will not stop ringing until the fax's failed. Hope you change this that if the number is for voice only and someone attempted to send a fax to it, it should no longer ring and the fax will automatically fail.
I don't believe RC, nor any phone system, can distinguish an incoming call from a phone or a fax (unless a Distinctive Ring process is in place). Don't know if RC is capable of that - maybe someone here does.
Faxing is essentially just making a call, and when it is answered, it sends tones to signal the other side that it is a fax. Unfortunately, I don't believe changing that setting to voice only will eliminate the ringing (it can't because the system simply sees an incoming call). It just means you can't receive a fax at that number. Hope that helps even though it doesn't solve your issue.