This is not going to make customers happy …

If you purchased a GSG 5 SD model with a barrel shroud (Fake Suppressor) ATF has now determined that this is regulated by the NFA and must be replaced.
To all retail customers:

On January 2010 American Tactical Imports Inc received official notification from the Bureau of Alcohol, Tobacco, Firearms and explosives that the original barrel shroud (aka: fake suppressor) supplied with your GSG 5 SD model must be replaced. It has been determined that this shroud is regulated under the National Firearms Act. American Tactical will provide a replacement shroud at no charge for each GSG 5 SD model sold or currently in inventory.

More info at Gun Trust Lawyer.