At the beginning, minor noise emission is normal and will disappear after a few hundred miles.

If the frame is a big volume aluminium case, it can act like a violin body and amplify the smallest sound!

If noise appears after many thousand of miles and is in direct drive only (when high or low gear aren't engaged), the planet gears may run dryly. Please insert some lube.

General comment: the longer a planetary gearing system runs, the smoother and noiseless it will be.

In direct drive of mountain-drive, the planet gears are running without any load. They may generate little bit more noise than in geared-down mode, when load is on planets.