Well, to me the answer could be one of several things. On the one hand I've heard and experienced first hand that some spirits tend to want to communicate. When they find someone who they can communicate with and they recognize that they're being heard they will step up their efforts and will flock around you to try to be heard. Also sometimes it may attract others who see the opportunity to be heard and cease the moment so to speak.
Some would call this "Opening a doorway" or "opening a portal". To me its less a portal and more just providing an opportunity. Its the same reason that spirits tend to flock around those who are sensitive, and those who can hear them.
So as such its a possibility that by providing the EVP on a regular basis, you've been seen as that opportunity and have attracted some attention. Its something that all paranormal researchers must be aware of and prepare for. We create the spotlight, and must be prepared to deal with the results.
Its why they warn of Ouija boards and skying or other methods of communication. Its also another reason investigators seldom investigate in their own homes. You don't want something attaching to where you live. You've heard the old saying, don't @#%@# where you eat.
But another option could simply be that, since you're now listening for signs and becoming more aware you could be interpreting some normally unrelated events. Its always good to have someone with you during all investigations. It prevents hyper-sensitization and gives you a sounding board at the same time. There is strength in numbers.
