This is completely normal. When using activated carbon filters, this is common and can often be expected due to the initial absorption of compounds in the filter. This is normal and not harmful in any way. The odor should subside within 1-3 weeks depending on the flow setting your units are running at. The smell is often related to the humidity level of the room in which the unit is placed. The more humid the environment, the stronger the smell may seem. Carbon filters are great for absorbing odor-causing compounds but may not always be needed in your particular application. Some are more sensitive to odors than others and we understand that. If the short-lived smell is too much of an inconvenience, you can always use an additional antimicrobial filter in place of the carbon filter. We will be more than happy to help you work through the best option for your application if you give us a call.