Hi a noise came into the engine of my astra .I thought that the drivebelt wwas slipping but changed that .Then i checked all pullies worked by the drive belt.I took off the belt and ran the engine but the squeeling noise was still there .The noise was coming from the oil fliter/turbo area .I contacted the main opel dealer and they told me it sounded like the turbo was the fault.I got a local mechenic who said it was the vaccum control valve connected to the turbo or the turbo its self .I got it run through a dionostics test and the guy said it was showing air pressure drops and it was the turbo.I replaced the turbo vaccum valve changed the oil and filters checked feed pipes etc made sure everything was spot on .But when i started the van the squeeling noise was still there just as bad .Anyone have any ideas ? I really need the van and this is losing me work