I know this thread is a bit old, but I still give it a try as it is kind of a follow up on my original post:

When I bought my PodX3pro back 2 yrs ago, I tried to hook the pod up to my Mesa Boogie Mark III with the 4 cable method. I didnt really get satisfied, mainly because of an anoying "buzzing" noise when using the hot/hi-gain channel. Therefore I ended up using the pod mainly through a couple of activ speakers. That has been working fine for me, and besides I get to use exactly the same tone as when recording via the SPDIF out on the pod.

Eventually, however, I`m beginning to miss the tone from my tube amp, and I`ve been giving the 4-cable method a second, and more serious try. I`ve now wired the pod to my amp like this:

Guitar --->  Pod input (guit 1-front),       Pod loop send ------>Boogie guitar input,    Boogie  loop send ------> Pod loop return,      Pod 1/4 inch output ------> Boogie loop return.

I`ve played with the pods loop send and return levels so the signal strength from the"pods loop-send" matches  my guitar input, and that the overall output level from the Boogie is aprox the same as when using the amp alone. I`ve also tried putting the loop in a pre- and in a post- position.

The positive thing is that I get a really satisfying sound/tone. The Tube distortion from the amp as well as the "punch" from the amps speaker is just the same with the pod connected as it is with the amp alone. And I get to use all the effects in the Pod in whatever way I wish.

BUT:  There is a really anoying "buzzing" noise from the amp which is not present when the pod is disconnected. The noise is of a more high frequency than what is discribed as a "ground-loop- hum". I`ve done a lot of testing and my conclusion is that the noise originates from the pods loop-send. I`ve tried the following wiring;

Guitar -------> Pod input (guit 1-front),    Pod loop send -----> Boogie guitar input

This setup is like putting the Wha-pedal, noise gate and other pre-preamp effects of the pod between the guitar and the amp-front input.

The noise is still there, meaning that it is not genereated by the tube-preamp sound traveling through the pod.

I`ve also made sure to use grounded "clean" power, and I`ve tried several combinations of switching on/off the "ground-lift" of the Pod, and the "Ground A-B-off" switch on the amp. There is no difference in the ammount of noise.

It is not really acceptable to use the amp and Pod in this way as long as this noise is present (even if you dont hear the buzzing while playing).  It is kind of frustrating not beeing able to get rid of this obstacle, as I feel that I am very close to success in having a really great setup. I hope that there is someone out there who knows some "magic" that helps.  I would be grateful for your comment