If the ticking isn't completely tied to the engine RPM, you could have pre-cats that are starting to crumble. They usually sound more like BBs in a can but could sound something like a tick. Try putting a large screwdriver blade on the precat(s) and 'listen' to the handle to see if the noise is coming from the precats. Open the hood and rev the engine slightly by hand to see if the sound follows the engine speed closely.
