And a quick way to fix that if it really bothers you is to turn on the subtitles. The lack of difference in engine tone until the gear is dropped is a little annoying, but that's not really a problem for me. But I must say this is very impressive. As many other reviews said it takes some power to run this game. Well worth the money.
Campaigns are great.
The manuals could have been a little more helpful but just take some time in some easy missions and fiddle with the weapons systems, you'll figure it out soon enough. My advice is take about a week to learn all the controls. Don't just jump into a campaign mission and expect to win. That's all it is. Training misisons are a breeze compared to the campaigns so learn from em.