Rattle from engine, loss of coolant, burning smell?

[Stan_D]

Would appreciate some ideas on what this might be before I go to the mechanic next week:

1. Rattling noise coming from engine area noticeable when driving. No warning lights.
2. Got home: rattling noise louder on the right side of engine.
3. Burning smell from right side vent.
4. Next day: checked oil & coolant level. Coolant was low: put in 1.2 litres.
5. Coolant started to leak soon after refill, on the right side, under the engine.

Should I be worried or really really worried?

Thanks.