If its wobbling in different speed bands like 80-100 it wobbles, then 100-120 it doesnt and then again 120 - 140 it wobbles. This is completely because tires aren't balanced. Get your tire balance and it will be fine.
If rattling in engine what you say is precisely rattling sound of something is vibrating in the engine, then better seek a mechanic help sooner than later. I doubt it could be some loose belt pulley which is making noise only on high rpm = high speed, or something else mechanic can only comment by seeing it or hearing it in person.