need advice--whinning nosie from engine if drive at low mph for >30 min

[rubs]

I am trying to find a exact problem that the car is having for last few weeks and now i am sure that i know the symptom and needs advice on what can be the possible issue and how to fix:" After i drive the car on inner roads for about 30-45 min at <35mph, engine start making knocking/rattling/whinning continuos noise and i can feel the shake in pedal and steering and it feels like just to stop the car. This does not happendif drive less than 30 min on inner roads and never happens on highway driving for 2-3 hrs at >65mph"Any advice or suggestion will be appreciated.car: 2001 i30 having about 56k miles

Thanks--rubs