I have an Astra 1.8 Design Auto on a 56 plate that I bought via Network Q dealership at the beginning of the year. It has been back to the garage numerous times to investigate a high pitched whistling noise coming from the engine when the throttle is engaged. This is most noticeable around 40mph and stops the moment you take your foot off the throttle. It occurs whilst keeping the speed constant and accelerating although most noticeable at a constant speed. There is no noise when stationary and engaging the throttle. Whilst the dealer have tried to find the cause they have now decided that it is a feature of this particular model and they all make this noise. I find this rather hard to believe. Does anyone have this model and can you confirm if you suffer with this noise? Any ideas on what it could be welcome as Vauxhall don't seem to know! Thanks.