Those little Yamaha and Roland portables with built in speakers are under rated in my opinion. Plugged them into a PA system or powered speaker and they come to life in a surprising way. The built in speakers are great for practice, on stage monitoring and just to get you by when that's all you need. But, when you try them out in a store ask if you can connect them to a stereo PA or even a decent mono powered speaker. I think you'll be surprised.
This opinion is presented by a guitar player/singer that does not play keyboards or pianos. I'm going by what I experience from listening.

Does the noise in your head bother me ?