It could well be the timing belt.
You don't need a strobe to check that (strobe is for your ignition timing). If you look in your Haynes manual it should give you a procedure somewhere for getting your engine to TDC and checking your static timing i.e
crankshaft pulley mark is aligned with the arrow on the lower cam belt cover, camshaft pulley mark is aligned with the top of the head etc.
Failing that try 'golfvr6' suggestion with the knock sensor.