Rangehood ducting is essential for the ventilation of the kitchen area. Removal of cooking fumes enables fresh air to replace the steam, oils and odours that would otherwise be distributed around the home, settling on walls and suraces and permeating carpets and fabrics. Yet although essential, in this writer's long experience, complaints about excessive rangehood noise have been tracked backed to the ducting. A poor ducting installation can ruin the performance of a perfectly good rangehood by causing obstruction and back pressure.
Too often inappropriate duct is used for the installation, usually the floppy (nude) plastic duct that isn't really suitable for fast moving air under pressure. Avoid this at all costs. Soffit ducting can sometimes cause problems because of building design. The narrow angle roof pitch of many modern houses often doesn't leave enough room between the top plate and the roof for adequate-sized duct to squeeze through.
The way most installers overcome this is to use floppy duct and crush it so that it will fit through. Unfortunately crushing the duct reduces capacity, especially for more powerful rangehoods, resulting in more air resistance, back pressure and noise. If your home has a shallow roof pitch you might be better of ducting through the wall or the roof; both of these choices will give better performance than a bad soffit installation.