My 156 2l Sportwagon just started to emit a droaning (moaning) noise a few days ago whilst cruising down the highway. That's when I called Alfa in Toulouse and found out it might be due to a lack of Tutela.
The funny thing is that it doesn't seem to be related to any particular condition. It comes on intermittently at any speed, in any gear, at any RPM, in any attitude (cornering or straight line, braking or accelerating) and suddenly disappears for a minute or an hour before reappearing. Other than that, she runs like a Banchee.
The Selespeed oil level is fine, and the tires are a good 5 mm away from the wear indicator all around.