jim,
make sure that there's only 1 device in your setup grounded (by preference, the mix desk if you use one.
Separate electric wiring from audio cables. they can't touch each other.
The voice device surely can cause some hiss.
Power supply? is the electricity stable? peakes and spikes (Distortion and parasites in the power current).
Any of the mentioned can cause distortion and even a loss of audio quality.
Yes it goes that far and even further in audio recording.
regards
chris pax