weird noise when turning in reverse

hi, i am getting some weird da da da ( it's something like that) like noise when ever i am in reverse and i am turning either left or right and it seems to only do it when the power steering turns on. and it only does it in reverse not in drive and this is a 96 saturn sl2 auto with 72k miles on it. and recently i had a new alternator put on and it seems to have started from that i thought that but when i check the belt tension on the belt it is tight. like can't move it tight. and i did check my power sterring fluid level and it was fine. so any help will be apperacted.

You a nice mystery. Nothing obvious comes to mind. How fast is the repeating nature of the noise - at about the speed of engine rotation, or slower, like a tire rotating? And how loud is it. Does it happen only when you are moving backwards, or can it happen when in reverse, with the wheels turned, and the car -not- moving? Does it happen if you are backing up and dont have the wheels turned left/right at all?
If it started after you had the alternator replaced, I could suspect the alternator didnt get reinstalled with both bolts tightened, and it is moving around under the extra load on the serpentine belt that comes from use of the power steering. Or even that the power steering pump is not tight. If they loosened the power steering pump as part of the alternator changeout - its not easy to get all of its bolts back in.
If the serpentine belt tensioner was going bad, and not keeping proper tension on the belt, would the skidding of the belt (due to high loading of the power steering pump) happen in a periodic surging matter?

it happens at idle which is around 700 and i started to notice that it also does it in drive but again only when the power steering seems to turn on if i turn the wheel all the way to left or right about 3/4 of the way of turning the steering wheel that is when it will start to make the noise but stop once the well is all the way. and only does it when turning. is it possable that it is the tensior making the noise.