Low frequency sound rumble

Hello everyone, I have a 2021 grand Cherokee limited 4x4 with v8 and Quadra drive 2 without air suspension. I bought the car used, but i also have a 2014 grand Cherokee ltd v8 but with Quadra trac 2. My older car doesn’t have that weird sound, The sound starts with low speed and when the roads are bad the sound is more pronounced. Was thinking on tires, and already changed with new ones, also replaced the struts/shocks with new ranchos. And still have the problem.. could be the diff oil? Car have 40.000 miles. Previous owner changed the transmission oil/filter, could be the transmission that need oil? Because sometimes, when I’m driving normally and arrive to a stop light, the transmission doesn’t start in 1st.. instead, start in 2nd. Lot of issues with a relatively new 2021 in comparison to my 2014.. the previous owner was my neighbor, never tow anything or something like that.