Q: Location of the cabin filter and rocking noise underneath vehicle. Gas guage keeps going up and down

I was browsing the internet checking out air filter for my van. I came across that my van has an cabin air filter. I went out to my van, which i bought used, and cannot find where it is located. It says it is located underneath the passenger side glove box, but do not see it. Where else can it be locate?

Ever since I had my van, I hear a rocking noise underneath my vehicle when I go over bumps in the road or sometime for no reason. Someone told me it might be the engine mount is loose, but I am not 100% sure that is the issue. Could it be that the mounts are loose or another issue? Also, when I go over bumps in the road, I hear a small squeaking noise underneath the left side of my vehicle.

Another issue I am have is my gas guage in the van keeps going up and down, so I do not really know how much gas I have in the vehicle. This has been going on for a while now. What can be wrong here? A sensor gone bad?

My car has 197000 miles.
My car has an automatic transmission.