Rattle noise at low rpm

So I have a 2014 Prius c and it has only 98k on it. I recently started noticing a rattling noise that what sounds like is coming from the engine at low rpm’s . It’s only when I get right from EV into the eco mode when the engine kicks in (I have put a obd2 in to see the rpm’s when it’s happening so I know it’s only at low rpm’s) Once I speed up , it’s gone. I also have slight knocking when I first start the car not sure if that relates to this but it sounds similar . I recently replaced sparks to and it didn’t solve anything