Problem with 1600n Fax setup and telephone answering machine

Does anyone have this problem?  I have properly connected my tel answering machine to my 1600n fax setup. Everytime I hang up the phone after 20 to 30 seconds I get a secondary ring which is most annoying.  I have a vtech ip5850 telephone machine. The line seems to be open to the fax for a few seconds after I hang up on a call and therefore I get a second ring.

 

If someone know whether the problem is the Dell 1600n or the telephone answering machine and how to solve this annoying problem please get back to me,

 

paffer