My MY96 Impreza Turbo has started a slight ticking noise - seems to disappear above 1500 revs but it's annoying. Just had bonnet up and there is a clicking from top centre of engine but I think the main culprit is a little cylinderical canister mounted next to the MAF - has 2 or 3 vacuum pipes running from it. It is ticking away when you blip engine and you can feel the vibration from it. Probably why the noise seems louder from drivers side window when driving slow.
Anyone help? What is it? Is it serious? Cheap to replace?
Also, top end ticking - anything to worry about? Done a search and seen tensioners, injectors and the like mentioned.
Car has 75k on the clock and run's superb (touch wood) Will need a clutch soon though

 

Thats the boost solenoid, its supposed to tick as it opens and closes

 

Thanks Davey - would it get noiser or have I just not noticed it before (don't have the windows down too often up here in the North) Only had the car 3 months so still a bit new.

 

once it's ticking, you know it's working !