C# - Writing String To A File Is Generating Unexpected Content?

I've two Strings which I'm loading from a SQL Server 2008 database (nvarchar-field)After loading them from the database Visual Studio 2010 displays them as follows in the watch window:

str1 = "Test"
str2 = "Test"

But the comparison with str1 = str2 returns False If I write those strings to a file with UTF8 Encoding the result is as expected:

Test
Test

If I write those strings to a file with ANSI (Default) Encoding the result is NOT as expected:

?Test
Test

Converting the strings to bytes:

System.Text.Encoding.Default.GetBytes(str1) 'Returns ByteArray {63, 84, 101, 115, 116}
System.Text.Encoding.Default.GetBytes(str2) 'Returns ByteArray {84, 101, 115, 116}
System.Text.Encoding.UTF8.GetBytes(str1) 'Returns ByteArray {239, 187, 191, 84, 101, 115, 116}
System.Text.Encoding.UTF8.GetBytes(str2) 'Returns ByteArray {84, 101, 115, 116}

Where is the Byte 63 in case of ANSI Encoding OR Bytes 239, 187, 191 in case of UTF8 Encoding for str1 coming from?Well, Bytes 239, 187, 191 are the BOM for UTF8. The question here would more likely be: Why do I get the BOM for str1 but not for str2?(Well, the values are values passed to a webservice which inserts them into the database, the initial values are passed to this webservice by a client I've no control over)