A rack mounted PC would be nice, I've put all my stuff in one box but the PC was seperate in it's own tower case. I've had no noise problems with mine.
Just keep power cables physically seperate from signal (segregation), if they do need to cross then do it at right angles to each other, then you need to obey the guidlines for;
earthing, screening, manufacturer installation instructions for all components, cable types and sizes, magnetic shielding(PSU transformer), I'm sure there's more.