I'm sorry to hear your washer has a stale smell. Odors are usually caused by bacteria introduced to the washer from the home's water supply, the dirty laundry, and other environmental factors. There are some basic maintenance procedures that can help prevent these odors from developing.
The WF331 is equipped with PureCycle, a pre-programmed cycle that helps to clean the drum inside and out, and should be used after every 40 loads, or approximately once a month. This cycle should not be used when there is laundry in the washer. For more information, please refer to the User Manual, which can be downloaded as a pdf file from this website.
Wiping down the door and gaskets and washing out the detergent drawer with warm water periodically can help, as well. It is also very important to use only the recommended amount of HE detergent to help prevent oversudsing which can lead to odor because the suds can leave residue on the drum which traps bacteria. Samsung also recommends cleaning the debris filter, which is accessible through the panel on the front of the washer. Instructions for cleaning the debris filter can also be found in the User Manual or by following this link to view a short how-to video: http://support-us.samsung.com/spsn/...