Thanks for the responses guys. Tom, what you said in the last sentence in your paragraph has also been on my mind all last night.

Well, I have an Emotiva XPA-3 coming to me by the end of this week which is beefy enough to supply a 400 X 2 stereo load at 4-ohms. So, if it is still making the noise I am definitely going to suspect a pre-amp configuration. Any other ideas?