Prius NHW11 startup question.

Recently, when I start the engine (cold or even warm starts) I hear a subtle knocking noise that doesn't last too long but a few seconds. I figured that maybe it's because our area may still be using winter mix gasoline... but I'm not sure. Also, there's a rattle underneath the car when the engine switches into generating electricity with MG1. This only happens after a start-up procedure (cold or warm). It stops when I push the gas pedal down a little bit (while still in park) then it goes into charging again, and by that time, it's stopped. I figured it may be a heat shield on the exhaust. It sounds more up in the front.

Also, when I start the car, the engine starts smoothly but then 1-2 seconds later goes into spinning MG1 which makes the car kinda sound like "vrrrrrrr---VRRRRRRRRrrrrrrrrrr...." Sorry for these dumb questions, I'm more used to the second generation Prius, honestly. Thank you in advance!

 

I have the torque app for my Android, if that's any good.
Also, It hasn't knocked in a few days but it did tonight when I started it. It lasted only 2 seconds or so. No warning lights at all, so no issues.

 

Bringing this thread back because I now have a 2002 Prius again, with 152,000 miles. The engine knocks after startup. Warm or cold. Only knocks when the display shows its charging the HV battery after startup, then goes away when charging stops (still in park) and doesn’t come back at all during driving unless I shut down the car and startup again. I’ve listened closely and the noise seems to come from the right passenger side of the engine. I’ll try to post a video.

Also, records from Toyota show the previous owner had the spark plugs replaced at 12X,XXX miles, inverter coolant and engine coolant replaced also.