The story about ownership of sounds (in this case kazoos that simulate duck quacks) has been pretty widely covered by a number of folks who have some professional/legal foundation for pontificating on the subject. I'll say that it's a terrible idea and admit that I didn't know that it has existing precedents:
Cynthia Lynch, an administrator for trademark policy and procedure for the United States Patent and Trademark Office, said such sound marks were fairly uncommon, with only about 150 registered, a short list that includes the Ride the Ducks quack, the MGM lion’s roar and NBC’s signature chimes.
The truly scary part is that given the filed trademark their legal action seems (again, not a lawyer) legitimate since the business they're in dispute with is in precisely the same industry. The legitimacy question here is really with the Patent Office for allowing this filing in the first place.