It sounds like 60-cycle hum. Check that the power source you are using to power the phantom power unit is grounded properly. Try different outlets in your house as well. While it's all hooked up try moving cables around to see if there is a change in the sound of the hum. That could indicate poor shielding on the cables. Move the mic itself away form the ...
You need something to separate the send audio (you) from the received audio (the person being interviewed). This is done with a "hybrid" adapter. For example a device like the JK Audio Autohybrid. It provides a way to record only the received audio and a way to feed audio into the phone line.
It sounds like it could be one of several possible causes:
An effect used in the signal processing during playback. Without
knowing what your playback system is, this is just sheer guesswork.
Bleed that was imprinted at mixdown time due to simple channel bleed or due to signal processing
Are you using active monitors with dedicated signal ...
If your laying back the tracks in Quicktime you want them to be assigned to "Lfet" "Center" and "Right" no panning involved. Otherwise maybe you have some divergence or bleed on your center channel feed.