How do you fix a Whilpool Duet frontloader GHW9400PL0 that is loud during the spin cycle?

drain or drain pipes blocked
bearings gone

That is a common occurrence with dryers such as this one. Even though it sounds bad, it is harmless. If it really bothers, you can re-balance the load and it should reduce the vibration.

LOT OF THINGS TO CHECK, THE BELT LOOSE OR WORN, THE CLUTCH, THE TRANNY, THE BEARINGS BOTH TUB SEAL AND BEARING, THE REAR DRUM BEARING, the balance or counter weights.

THE DRIVE PULLEY- If the washer is making a loud noise the drive pulley might be worn out, cracked, loose or bent. Remove the drive pulley and inspect it carefully. If it is damaged or defective replace it.
THE TRANSMISSION, THE MOTOR COUPLER, THE MOTOR DRIVE BEARINGS,
THE DRIVE MOTOR- If the washer is making a loud noise the drive motor bearings may have worn out. Washer motors are normally almost silent when they run. If the motor is run without a belt hooked up to it and it's loud it will have to be replaced.
The drive coupling connects the motor to the transmission and consists of two plastic drive forks with a rubber coupling between them. One of the drive forks is attached to the drive motor shaft and the other is attached to the transmission input shaft. As the motor shaft rotates, the rubber coupling between the drive forks absorbs the torque to prevent the forks from breaking. Normal use will create wear on the coupling and eventually the drive forks may slip and cause a vibrating noise. If the transmission seizes or if the spin basket cannot turn freely, then the coupling may fail and again you may experience a vibrating noise. Most models will require you to remove the cabinet to access the drive coupler. Disconnect power from the appliance before attempting any repairs.

If the washer is making a loud noise the drain pump might be going bad or might have something caught in it. Remove the drain pump from the washer and inspect it carefully. Look for anything that might be caught in it, a piece of wire, plastic, etc. If nothing is wrong with the pump, but it's still noisy it will have to be replaced.

Front load washers often use a self contained electric drain pump and the motor may be worn or damaged and require the complete pump to be replaced. Remove any foreign objects or replace the worn or damaged pump, thencarefully tighten the hose clamps and check for leaks before installing the cabinet or front panel.
All front-load washing machines have shock absorbers that are used to dampen the tub movement in the spin cycle. The shock absorbers or struts are attached to the base frame and to the outer tub and you will need to remove the front panel or the rear panel to access them. When shock absorbers weaken or become damaged, the machine will often make a loud banging sound during the spin cycle and if the symptom is not corrected, can lead to damage of other components. Inspect the shocks for signs of broken attachments, leaked fluids or a weakened dampening action and replace both shocks if worn. Remove power from the appliance before attempting this repair.

Some models of top-load washers use tub dampening straps to cushion the movement of the tub during the spin cycle. There are four straps attached to the top of the tub and to each corner of the cabinet

Also There are four suspension rods that suspend the tub and allow the tub to free float. If the suspension rods are noisy, there will be a squeaking noise during wash. You can fix this by putting bearing (lithium base) grease in the cup that each rod rests in. If it continues to squeal replace all four rods the cups come with the rods, replace them as well.
If your washer has a loud banging noise during spin the balance weight may be loose. This weight is to counter act the weight of the motor so you will find the weight directly behind the motor. Sometimes simply tightening the bolts will fix your issue but if the bolts are stripped out get some bolts slightly longer than the original bolt to allow you to put a locking nut on the bottom side of the mounting plate. If the weight is broken replace it.

Lastly Washer vibration can be caused by a broken counter balance spring. Ur washer may be equipped with one or more counter balance springs which help to absorb the natural movement of the spinning tub. If a counter balance spring fails the tub might lean in one direction more than another and it will shake and cause vibration.

I'm having the same issue. It's as if the drum is off-balance.

The problem might be that your load is off balance and the adjustable feet are not set properly to set the feet you will need a level and all you have to do is twist the wheel until the bubble is in the center you may have to just do the front and back or one side

Their is a auto balance circuit in the machine. it a sensor, it will adapt the machine... you may have a failure in this machine....

Sounds like the drum, balance weights have come off, to me. This will cause those symptoms.

I have the same problem. During the spin cycle, the washer spins all over the room.....very loudly.

are you sure your machine is balanced and installed on a sturdy foundation?

If the washer is brand new, look on the back panel and make sure the 4 transportation bolts have been removed. The bolts should be roemoved completely - they are only necessary to protect the washer during transportation.

If the bolts are removed, adjust the front two legs to be 1/4 inch higher than the back two. That 1/4 inch will balance the washer during the spin cycle, perfectly.