2011 Hyundai Sonata Engine rattle

Hi,

My fiance has a 2011 Sonata that for the most part she's been taking care of. However I've recently found out that she overlooked her oil change date. The first issue occurred whenever you pressed the gas and revel told high you would hear a rattle and smoke would come from the exhaust. So I went to get it an oil change and the technician let me know that it would need an engine flush a well which I opted to put on hold because I didn't have the funds available. After the oil change however I've noticed that the rating noise and loss in acceleration happens at much lower rpms now. Does this sound like a problem that an oil flush would fix? Thanks!