Norcold frig has/requires a fan if the unit is mounted in a slide.
I would imagine that Dometic needs the same. The reason is that a slide mounted fridge vents horizontally through the side and doesn't vent as well with natural thermal convection.
My Norcold has a thermostat that turns the fan on, I believe at 100 degrees. Fan failed last year and caused the frig to error, causing a bunch of headache while on vacation. I replaced it and added a second fan that is manually controlled just as a standby or to help on really hot days.
Your fan shouldn't be too loud unless it has a bad bearing.
I bought 2 replacements with same specs as the original, except for lower current draw, on ebay for $16 last year.