Some centrifugals won't run (long) in reverse rotation. Others will do a surprising amount of tonnage when running backwards. I've had the pleasure of diagnosing a handful of machines that were placed into operation in reverse and left that way, one of them for several years. That one in particular did 6.5* out of a rated 10* delta T when running with the vanes wide open at rated FLA (or as close as it would get). It also had some SERIOUS discharge superheat going. As far as unusual noise, they've all sounded somewhat odd, but not enough so that I would have said that there was a problem in the compressor just because of the sound. That said, I've never had an FA with that problem, so I can't say specifically, just generally.