P148F & slight rattle/shake on startup

Hi! Thanks for all the help!
I have 2013 Prius, just got it a few days ago. Drive it the first few days and no trouble.
Still drives good but...
-started to shake & rattle for maybe a second sometimes when I start it up or leaving a stop light with AC on.
-no check engine light on but tech stream does show P148F code.

Where should I start? Due to the rattle is the head gasket bad?

I really appreciate your help!
Jim