I have a 2010 Mazda3 hatchback & earlier this year I turned on the radio and had this very loud machine-gunning noise coming out of the speakers. Investigations showed the amp had blown up & these are under the passenger seat. Determined to fix this myself I looked into new amps. I could buy one from the dealership for ~$500, buy a used one from eBay for ~$300 or send it away for repair for $175. Then I called Bose. The nice customer service lady told me this is a known issue with these and that they'd send me one for free, which they did. They didn't even want the old one back. First I disconnected the battery. Replacement involved removing the bolts holding the passenger seat to the the floor, leaning it onto the back seat and removing the cover plate. Replacing the amps was just plug and play at that point. I had the whole thing done in an hour.

It turns out Bose will do this: if you have one of their products that has gone bad they will replace it for free. Impressed I am.