2005 Echo Hatchback
 

Need a little bit of crowd sourcing to figure out what my recurring rust issue is on my Echo hatchback (see signature).

I keep finding insane amounts of rust on the drums every spring and fall when I change my tires. I consider myself someone who takes decent care of the car and I don't do too many miles per year. The car is parked underground in the evenings and in an open air lot during 9-5 work hours.

Everytime I take this in for service, the rear drums are always a topic of conversation and since I've personally seen it myself, I don't think the service dealer is lying to me.

Any ideas?

Off topic: for those of you who are going to chastise me for taking it to a service dealer, it is by far the most convenient and non-obtrusive way for my car to get worked on. It happens during my in-office hours and doesn't force me to take time off or weekends off to get this work done and no I can't bum a ride off someone.