DIAGNOSIS That rattling/buzzing is almost always the condensate drain pump, which is located in the lower rear of the cabinet. The little impeller inside can get jammed by mineral scale or a small piece of debris, or the pump motor itself can start to fail.
FIX Unplug the unit. Remove the water bucket. You'll see the pump housing at the back of the bucket cavity. There's a small removable cover (often with two screws). Remove it and check the impeller for obstructions—lint, scale, etc. Clear anything out. Manually spin the impeller to see if it moves freely. Reassemble and test.
IF THAT DIDN'T WORK If the noise persists after cleaning, the pump motor bearings are likely shot. You'd need to replace the entire pump assembly. The part is often listed as a "condensate pump kit" for this model. It's a plug-and-play component, so if you're handy, you can swap it yourself by disconnecting the old pump's hose and electrical connector.
HEADS UP If you're not using the pump (i.e., you're just using gravity drain or the bucket), you can actually unplug the pump's electrical connector inside the unit to stop the noise entirely. Just know you won't have pump function until you reconnect or replace it.