Katar Diamond (no relation) say's in her excellent book, "Feng Shui for Skeptics," that it is a myth or superstition that having a bedroom over a garage is a reason for concern. In her experience of doing thousands of Classical Feng Shui audits, there is no effect she has observed of having a room where you spend a lot of time over a garage (p 118). I would think the flying star relationship would be the important dynamic to consider, as well as noise from the garage door opener and possible auto exhaust fumes.