The exhaust tone on my Astra 2.0L 16v GSI is making a horrible rasping noise when I am at about 3000 rpm, it sounds like metal touching metal and vibrating (I have checked and found nothing). Would one of your manifolds remove this problem?
It is obviously very difficult to diagnose a noise without actually seeing the car. Certainly the 4 wheel drive and 2 wheel drive Cavaliers produce a noise such as you describe (whether it is the same noise without seeing the car, I would not like to guess further). The noise we know of is caused by the induction and the exhaust pulses producing the rasp noise you described at a specific rpm. There is nothing normally wrong with the noise and it does not affect the performance of the engine as such. Changing the exhaust manifold or indeed exhaust system, or both can sometimes alter the point at which this noise occurs and sometimes even reduce it. But I would not like to guarantee that. Our exhaust manifold would certainly improve the performance of your car. We have had reports from one of our customers who already has a free flow exhaust fitted to their XE engine in a FWD car and then fitted one of our exhaust manifolds and commented that he saw a 12bhp increase (we would normally only say a 6 - 8 bhp increase).