My 2001 Aurora is getting tired

I’ve riffled around this forum for a while so I thought I’d join and contribute a little. Anyway pleasantries aside, I have several issues with my Aurora. It is a 2001 4.0 with ~106K on it. Here are the issues

1) I’ve seen some posts on this before but I wanted to know if anyone else had input or relevant experiences. My check engine light is on, and the mechanic said it was the “secondary air injection system”. I haven’t noticed any performance issues, and other than the light being on I wouldn’t know that there was an issue. I would like to rule out this component since it is rather expensive to replace.
2) When I start the car in “colder” weather it sounds like I have something loose in the engine area. Specifically, drivers side inboard of the tire area. It only does it in cold weather and after it has been sitting for a while. Once the weather or the car warms up it goes away.
3) The car makes a noise when I make a compound left turn (I.E. turning into a parking lot from a main road where I encounter different slopes and angles all at once. The noise would phonetically sound like “shhhuk shhhuk shhhuk” and the occurrence of the sound is proportional to ground speed.
4) Finally, my passenger side/back seat area only blows out cold air when the heater is on.

I’ve done all the common sense things like change the fluids, check the fuses etc… I’d still care to hear even the most basic suggestion as I’m not a professional mechanic I may have overlooked the obvious.

Any feedback will be greatly appreciated.
Thanks