Need to replace heater core

[Jeepkj2022]

I’m going to take the plunge to replace the heater core in our 2012 Liberty. It’s about time to do it: cold weather around the corner. I was wondering if there’s a ‘best’ one to get: does it matter spending more money on one? Anyone have a particular brand they like? I bought a fairly inexpensive radiator on car parts.com back in May. Seems to be doing the job.
I also hear something in dash moving around, almost like a rat running around in the dash. Does it while the car is off too. Is this related to the heater vents? Any way I can fix this while I have the dash apart? I appreciate any pointers, thank you.