Hi there!
Some of my new GP7 made an eytraordinarily buzz more than the others and above the regular decoder hum.
At a closer inspection I found the reason and cured it easily.
The motor has some slack in its fittings to the frame halves and starts vibrating that is transferred to the shell and makes this model louder than it used to be.
A tiny drop of glue to the black plastic motor fittings stops the motors motion and just the usual humming is left.
Just wanted to tell and probably somebody can utilize this!
Regards
Mathi