Loud popping noise from under

I have 2007 Prius with 120k miles.

I started her up this morning with no problem, but as soon as the engine started running 5 seconds later, I started hearing very loud rapid popping noise from underneath. It sounded like it didn't come from tail end of the exhaust, but it was more from under the driver side. I turned her off and started again several times but the noise wouldn't go away. It just gets louder and louder until I turn it off.

Before this happened, I had p2601 and p1116 that I haven't fixed for more than a year. I had replaced coolant pump 2 years ago to resolve p2601 but it failed again a year later, so I didn't bother.

I checked the OBD again and now it also has p0446 (evaporative emission system, vent control circuit), on top of the other codes I have. Is this causing the loud noise?

I can't find any thread that closely resembles this. Any ideas or suggestions will be greatly appreciated.