Should a copper central-heating water pipe be mortar-ed in when passing through an internal wall?
That could definitely be causing a ticking sound if the pipe is moving it will clink against the mortar and possibly loud enough to hear.

There is nothing wrong with having mortar around it other than a PITA if you need to replace it.  What you need to do is make sure that the pipe is secure as possible (tie-downs, clamps, whatever) on each side.  You could also try wrapping the pipe in cloth to reduce sound or if you have a gap to hit it with spray foam.