If you remove the kick panel with a torx bit (3 screws), you can check
for anything unusual going on. Make sure that all 4 shocks are doing
their thing. If you have a loud knock in spin, you could easily have a
problem with your main pulley.
On those duets make sure that all 3 torx bits are tight because it adds
stability (albeit a little) to the unit. Also if it is on a pedestal
ensure that there is a rectangular plastic tab under each corner-this
isolates the rigidity to the 90 degree corners instead of the flexible
sides. If they are not there they could be in between the dryer and the
dryer pedestal as installer could have made a mistake. A 9400 would
probably be too new to have a spin bearing problem already. Make sure
that you use HE detergent with that and a fraction of what they advise. If
you are not using it make sure that you don't have regular detergent
visible if a factory tech comes out because they are able to void warranty
if they don't feel like working on it! There are also shocks on the bottom.
It's doubtful but one could be separated or even broken. Another
possibility is that there are some cement weights that add stability. I
have seen these break at the bolt locations. You'll need to get a service
tech out for that as it's quite a job. Whirlpool may cover even if it's
over a year. It could be "oil-canning" / when you hear the noise put your
hand on the side and see if the noise stops. There are some foam pads
between the stabilizer bar and sides that could be missing. Good luck!