Whistling noise next to alternator

[andreoz]

Hi guys, a quick question to identify the part and tell me if it is something to worry about. To the right of the alternator there is a cylindrical part attached to the engine (excuse my ignorance if I don't know what it is) from which I have noticed a whistling type noise eminating recently. What would it be and is it serious. My SVX has about 190K on the clock has had a new timimg belt put in some 10K ago and has been running beautifully. Any information would be welcome.