As RGWM it could be the valves rattling around which makes a terrible noise. If you havent used camlocks when stripping down the top end then this could be the problem or indeed one of the problems.
to echo again whats been put above the variators make the car sound like a diesel too but in order for that to be checked and replaced youd need to take the cambelt off but again with camlocks. Alfas are tricky blighters as on other car brands you can simply put a mark on the alignment of the cam and hopefully hold that in placed whilst you change the belts, if it slips then just line the marks back up. but with an Alfa this doesnt work so camlock are a must, without them it can ruin the engine.
If you do change the variator then change the whole cam setup i.e belt, tensioner and water pump aswell as the variator... if youd rather do the work yourself, camlocks are about £35 and the cambelt kit is about £85 although the variator may need to be bought seperate at about £80.
Id say check the valves to see if they are slightly bent, if so that might be the problem....
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