There is loud, high-pitch humming sound coming from under the hood of my 2004 Jetta 2.0 during extreme acceleration. And it doesn’t sound natural. It stops once the gears shift. Any ideas?
This is really hard to give advice to because there is not enough information and sounds can be coming from anyhting, which makes it mandatory to hear personally. This can be anything from a bad bearing in an engine accesory (Alternator, A/C pump, etc) to a bad timing belt or an intake manifold leak. If the noise comes from the area of the motor where the alternator is, then plan on it being one of the engine accesories. If the sound is a screetch when you first start the car for the first time of the day, goes away after warmup and then only screetches when you accelrate heavily, then it is the timing belt. If it is niether of those things then plan on spending big bucks to have the intake gasket replaced.