It looks like your character is U+0008, or hex-08 if you like. This character is not permitted in any XML document, so what you have there is not a well-formed XML document. Encoding doesn't have anything to do with it.
You are producing this document from a database? Then you will have to filter out invalid characters before writing the others to the document. And you will need to know which characters are permitted and which ones aren't. The
XML Recommendation tells you that; section 2.2 is the part
you should particularly read.