ratteling means a kind of "kdak" "kdak" sensation is felt in steering wheel while passing pothole or bumps. even though it is not much audible but feeling makes you think that something is getting disconnected from wheel or a loose joint.
i had same issue in my ford ranger but it appeared due to horrible abuse which a.s.s centre could not fix. they said it would require them to replace whole steering assy.
None of the Hyundai's are good handlers above 100kmph(don know about SUV'S though). The ride becomes very wobbly , bouncy , stability is not very inspiring!
I'm having the same problem with the i10. However this problem can be partially rectified with better tyres. Otherwise you can also go for an aftermarket suspension.
My Showroom guys and i20 brochure also tell there is no Magna option with ABS. Could you please confirm if it is available, so that i can opt for that.