That's terrible, sorry to hear that. For ZipCar's contract cleaners to be washing/vacuuming the car at that anti-social hour, the car is either in use all the time or the contracted cleaner has taken on more work than it can handle and is working around the clock. Having said that, the fact the alarm's going off regularly would hint at the car not being used enough.
In your shoes, prior to contacting ZipCar I would download the app if you haven't already done so, and look up the availability of that particular car over a couple of days, to be able to show ZipCar that there are far better times of the day for the car to be booked out and cleaned by the contracted cleaners. Failing that just check on the car a few times one day to see roughly how long it's there sat unused during daylight hours then contact ZipCar. If you are a member, you can call them from within the app.
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