When dealing with strange serial data like this, it can be helpful to print some debug output with the ASCII values of the incoming data, rather than the character equivalent (which may be non-printing). Serial.print() and Serial.println() automatically display the char data type as characters. If you want to see the ASCII code for the incoming data, you can cast to the byte type
Serial.println((byte)rc);
You can then refer to an ASCII table (the above code gives you decimal values):
The ASCII code for newline is 10.