Common fault
What is the loud humming or rattling from my refrigerator?
Short answer
Almost every new noise from a built-in comes from behind the grille, not from inside the cabinet where you hear it.
What is actually going on
A rattle or a buzz that carries on with the door open is usually the condenser fan, which picks up dust, pet hair or a stray piece of packaging, or whose bearing has worn. A steady low hum you feel through the cabinets more often traces back to the rubber the compressor sits on, which goes hard over the years and stops isolating anything from the millwork around it. A high whine that stops the moment the door opens is the evaporator fan inside the compartment, and that one deserves attention quickly, because the same fan is what moves cold air over the food.
What we check, and in what order
Noise is the one symptom worth acting on while the appliance still works. A condenser fan that rattles is a fan. A condenser fan that has seized is a warm refrigerator, a compressor that has spent a week running against high head pressure, and a repair in a different price bracket entirely. The window between those two states is usually measured in weeks, not months, which is why we would rather look at a noise than at what the noise turns into.
On the coast it is the bearing that goes. Salt air reaches the fan motor through the grille in Point Loma, La Jolla, Coronado, Pacific Beach and Del Mar, dries the lubrication out and puts a growl into a motor that used to be silent. It is a slow change, so owners tend to register it only after a week away from the house. Inland the same motor stays clean and simply runs far more hours through summer, so what fails there is blade balance and the rubber mounting grommets rather than the bearing itself.
If that matches what yours is doing, say so when you call — it decides which parts come on the van.
The wine cabinet under the bar held its number in the morning and was two or three degrees off by late afternoon, every day. He left a probe sitting between the bottles instead of trusting the front panel. Condenser was corroded and there was almost no air getting to that grille.
We only use the place part of the year and came back to water tracking out from under the fridge and a sheet of ice on the freezer floor. Not a burst line, the drain had frozen closed. He flushed it and checked the ice maker fittings while he was down there.
Growl coming from behind the bottom grille, worse after a week away. Fan motor bearing, dried out from the salt air he said. Same day, tidy, explained what he was doing and didn't try to sell me anything else.
Appliance down in San Diego?
Tell us the brand and what it is doing — we can usually name the likely repair before we arrive.
Questions
Answers before you call
The built-in is fifteen years old. Repair it or replace it?
Repair usually wins, and the reason is the cabinetry, not the appliance. Replacing means matching an opening, a panel front and the millwork either side, and in San Diego kitchens at this level the run was built around it. The usual faults are ordinary parts: evaporator fan, defrost heater, thermistor, door gasket, ice maker module. If one is not worth repairing, you hear that first.