I hear ya,,the knock can be of other reasons,
The 1.6 is a non-interferance vavle/piston relationship, but,,,,it depends upon the lower end relationship that creates the combustion,,,,so if the valves are not seating "completly" the cylinder wont seal completly.
A simple cylinder leak down test will confirm this. Its a matter of injecting air into a specified cylinder, while piston is at TDC and oth valves are closed,,,,if air escapes from the tail pipe,,,,an exaust valve is leaking,,,,if air is heard escaping from the intake manifold,,,an intake valve is leaking,,,
Most shops will charge you about $50 for a "cylinder leak down test".
This is the most accurate test that can be done,,,trust me..
If you have a compression gauge to where you can give me exact readings of each cylinder,,,,,we can REALLY narrow this down.
Let me know..