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My car is toyota corolla Runx, 2001 model, automatic.

from few weeks its making a rattling type of noise when in gear. its fine when running idle ( in parked or neutral). only when in Drive or Reverse, does it make this sound, sometimes its light, sometimes its quite significant. When A/C is on then its really bad. With acceleration (not with speed) it gets worse.

If its in "park" and i press accelerator, its fine, Only in gear it makes this noise.

i was trying to figure out where the noise is coming from, couldn't do that, but what i saw was that when i put it in gear (Drive or Reverse) the "engine block" tilts a little, this is when the noise starts.

Is it normal for the "engine block" to tilt a little when switching to gear from neutral.?

Any advise will be much appreciated.

Noises can be very difficult to diagnose without actually hearing them, so the advice here is to take the car to a mechanic to get them to hear it.
From your description, it seems that low engine idle speed (which is normal when idling in gear, and with A/C on) is causing a vibration resulting in a loose component rattling. It's possibly something simple such as an exhaust mount but may be something more serious.
It is normal for the engine to move a little on its mounts when selecting gear, but if it's rocking too much, an engine mount could be the problem.
Your mechanic should be able to diagnose this relatively easily.