Landline Drops Incoming Calls - Need Help Please !

This problem pops up every now and then, I've changed out the wires, phones, and connectors, even answering machines. Then it comes back months later. I have not replaced the phone jacks on the wall but I have opened one up and looked at the wiring and connections, all seems good. Nothing wrong there. Now the phone rings once and drops the call before I can pick it up. People redial and I pick it up real quick and I can talk to them. Calling out is no problem. I have my ATT internet thru my landline also, works fine. Any ideas would be appreciated.