Alright, so here's my problem (after a few relatively quiet months): my Alfa is doing a strange squeal / creaking noise at high speeds (e.g. over 150 km/h). I know such speeds are illegal in most places in Europe, but let's not lose focus on the issue at hand.
The noise is not rpm related, but speed related. On my 2.4 20v, 150 km/h corresponds roughly to 3000 rpm in 6th gear - the noise doesn't occur at 3000 rpm or above in any other gear. I don't have any strange noises when the car is idling, except some tick-tack from a broken exhaust bracket (to be fixed soon) and a barely audible noise from the aux belt.
The noise pattern is fairly irregular, sometimes it starts at 150 km/h, sometimes at 160 km/h, sometimes it goes away if I lift my foot off the gas, sometimes not.
From a vehicle state standpoint - water pump, cam belt, tensioner(s), idlers were replaced in January 2010; aux belt, tensioner, idlers were replaced in September 2009; the tires are fairly new (replaced this spring, Kumho KU-32 17", did less than 10k km so far).
Now the most likely culprits are either the engine tray (?) or the sunroof. The noise does seem to go away when I open the sunroof, but I guess it's obvious driving with the sunroof open at 160 km/h is far from ideal. I still can't tell if the noise is gone or it's just drowned in the wind noise when the sunroof is open. Any other ideas?