In my experience the P0420 code is more likely to trip when it's cold outside. Maybe in a couple months the code will go away long enough to get it inspected.
I installed KYB quick struts on my 2010 Civic about 2 years ago and they make a creaking noise when turning but only when it's cold out. Like single digits or less. 100% goes away when above freezing. 🤷♂️