2015 7300 carrie Reefer is loud compared to a 2018

So I have a real or legit question that I was curious if other have experienced the same? My dad and I switched trailers this week as we over booked ourselves and it was easier to switch trailers and keep rolling. My reefer that I pull 99.9% of the time is a 2015 7300 carrier and his is a 2018 7300 carrier. Only difference between the two besides age is hours. His has almost 5k hours and mine has about 16k hours.

What I am noticing is his is a bit quieter than mine. Least so it it seems. Anyone ran into this or have an actual explanation?

my reefer seems healthy. Doesn’t burn oil and cools off well but just seem like mine is louder.

 

I will take a look at those. Thank you

 

not sure? I know they don’t take def. mine won’t be carb legal come December.