Hi Hamer,
I've got a 3.2 Shogun and I do sometimes notice a groan from the front under the circumstances you described. I have put it down to the auto box still trying to drive the car forward. Unlike manual cars as one comes to a halt you dip the clutch and remove drive from the engine, with an auto box drive is always there albeit not fully due to auto slip. So what happens is as you reduce the pressure on the brake pedal the pads grip on the disc reduces and the vehicle starts to move forward,at this point the pads are still in a pressurised contact with the disc and a low resonance vibration is created. Brake squeal is basically the same phenomena only at a higher frequency due to higher disc rotation speed.
I also used to get the same noise from my automatic Omega and have experienced it in other auto cars when creepung forward while still applying a light brake.