"As my regular HVAC installer/service company I contacted Pacific Air regarding an "unusual" odor coming from one of the heating registers. They were out the next day and the tech told me that his experience was that rodents get caught in or near the register vents and subsequently "expire" which was likely causing the smell. While in this case he didn't believe that the critter was inside the vent, it might have bee close by. He then offered to crawl under the house and check, which he did, returning a few minutes later with a "bagged rat". Problem solved and for much less than even a regular service call. Can't say enough good about how Pacific Air has treated me over the years. Stand up folks you can trust. I highly recommend them."