Eventlog grows constantly with repeating message: Starting up database 'AdventureWorks2012'.

I'm not sure what I have done wrong!

I installed the latest SQL SERVER 2012 Expression (with Advanced Services) (SP1). Then I downloaded the sample Adventueworks sample database from codeplex. I copied the MDF to

C:\Program Files\Microsoft SQL Server\MSSQL11.SQLEXPRESS\MSSQL\DATA and attached it.

Now a weird problem occurs - my Eventlog grows constantly with never-stopping messages like this:

There are no error or even warning messages about SQL SERVER. I can use Management Studio to do query and all functions seem work fine.

Matrix is real.