We've got a Java SOAP client running against a GW 8.03 server that's getting the following error:

Caused by: javax.xml.stream.XMLStreamException: ParseError at [row,col]:[1,7342]
Message: An invalid XML character (Unicode: 0x1) was found in the element content of the document.
        at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(XMLStreamReaderImpl.java:594)
        at com.sun.xml.internal.ws.util.xml.XMLStreamReaderFilter.next(XMLStreamReaderFilter.java:81)
        at com.sun.xml.internal.bind.v2.runtime.unmarshaller.StAXStreamConnector.bridge(StAXStreamConnector.java:181)
        at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:349)
        ... 19 more
Apparently, the GW server is producing an illegal XML character. Are there any known causes of this? And is it a best practice to filter the SOAP response when it is returned from the server to weed out these kinds of characters?