Originally Posted by DJMala

First, almost all EVP recordings I've heard are very noisy and poor quality. I've rolled plenty of hours of tape in controlled conditions using high-quality mics, including recordings made with a portable rig in old churches and performance halls.

Perhaps the phenomena is electrical, being picked up by the microphone wires or the recorder itself. This is the most likely possibility. The major problem here is that cables and recorders are designed to reject exactly this kind of interference. If they weren't, you'd constantly pick up stray radio signals of all kinds.