Same on my 2004
Strange, I was login in tonight to ask essentially the same question. Also a 2004, now with 60K miles and expired warrantee.
When my AC system is "on" (auto or otherwise) and the system is in one of its "quiet" moods the sound is best described as hard disk like. Like when a disk is accessing data - a spinning, servomotor like sound when the armature sweeps back and forth. Initially I thought this might have been the NAV, but I now believe this more a symptom of the AC. But wait there's more.
After vehicle start-up and for the first few minutes of operation, it sounds more akin to a piece of wet rubber being pulled over plastic. Like a wet toilet-bowl plunger as it slips off the wet porcelain -- and just as feverishly as when I'm trying to get the Saturday morning double flusher out of the pipes. I jokingly said to my wife "... like a dog chewing on a rubber dog chew toy." Only this must be the three-headed dog from the Harry Potter stories and the dog chew toy enormous and covered in slobber. That dog will not give in.
The temperature slip from driver’s side to passenger side, one thought to be the problem has no impact. Temp high or low has no impact.
My best guess is there must be an air defector that moves back and forth to blend hot and cold air to combine and match to whatever the levels are on the thermostat. Some sensor or servo is dirty or failing.
This is intermittent, so until something brakes, catches fire, or gets so loud the cops are called, the meat puppets at the stealership will just keep charging me for repeat service calls --- basically what you just experienced. I hate going to the stealership without having the solution in hand, or the folks at the stealership just drive my T-reg around the block, charge me for their time and replace parts indiscriminately. Until I started having to pay for those parts, I as fine by me, but the gig on the warranty is up --- I pay now.
