First of all I have a QAD Ultra rest. Today when I was shooting I had three shots that were loud and I could see the arrow fishtail to the target and it hit about 6 inches off. What could cause this? I just got my rest moved up but I sighted it in before w/o any problems. Also I just added limb savers, a stabilzer, and a wrist sling right b4 I shot today. I hope that the loud noise is my arrow hitting something and not my bow experiencing the stress of a dry fire.

My guess is that the arrow fletch is hitting the rest

Thats what I thought too, but why not every time? Why the noise?

Make sure your nocks aren't coming away from the string at full draw........check to see if any are worn or loose and can be pulled away from the string too easily.
If you are at full draw and the nock is off the string a bit because of pinch or slipping?....bad.[:-]
Make sure they snap lightly but securely, and replace any that are worn cracked or different in any way.

I agree with Matt, start by checking your nocks for wear and proper alignment.

Matt when you say bad do you mean bad for my bow?

"Bad" meaning the arrow could come unsnapped off the string but not fall completely off. Not to mention wrecking any hope for accuracy, it could cause a dry fire and make the arrow whip around, making a mess of your personal tender parts. One of those 'damage to the bow and possible personal injury' things.

Also, are you sure you're not torquing the string or pinching the nock hard enough to lift it slightly off the rest?

Maybe a loose or not fully attached fletching / vane?

What about numbering your arrows to determine if it's the same arrow or not?

Of the QADs that I've installed, when installed on certain bows with short cable slide travel and faster speeds, will NOT drop fast enough. If you're using vanes rather than feathers, it's more pronounced. The spring tension can be increased and will most often correct the problem, but it is a cumbersome job.

This may or may not be your noise, but it's a start.