Re: 156 2.4 JTD Help Please
The aux belt tensioners on the 2.4 JTD's are well known for seizing and causing this squeeking/squeeling - often for just a few secs after starting.
It's a pretty bad design, the central shaft of the tensioner is steel - the pivoting body is an aluminium alloy!! - inevitably they corrode and join - making an adjustable tensioner into a fixed one!
replacements are expensive from the dealers - ie. well over £100, although Alternative Autos can supply a pattern version for about half that amount.
They can also be fixed though - the tensioner comes off the car easily, then you'll need plenty of lube and heat to seperate the steel pin from the alloy body - clean them up and refit - using some grease this time as mentioned above.
I posted a guide a while ago, with pics, on alfa156.net