I know the engine sounds have been changed recently, but they don't sound the best neither do they sound realistic. I think it's about time that all the planes in the sim have a engine sound overhaul. It will increase the realism in the game and there will be plenty of engine sound variation versus hearing the same sound for every plane. Depending on what engine operator each plane has, the sounds could be very unique from one another (747 with RR engines vs 747 with PW engines).
I'm not so worried about the prop sounds because they're perfect already.
The links below are a few videos of what certain planes in Infinite Flight should sound like, take a listen.
A320 and Family (they all sound the same)
(not my videos)
You should get the point now, all planes need a rehaul in engine sounds! :D