Hmm...
Are you changing your project tempo? If the Groove Clip plays back at the tempo it was recorded at (and no other alterations such as pitch or whatever have been applied) then it should just play back like a regular clip.
If you ARE changing your project tempo or fiddling with it somehow then what you are hearing is the "Online" rendering. This is inferior quality and is only meant as a reference for what your changes may sound like (such as stretching due to tempo changes).
When you are done then you need to use "Bounce To Clip(s)" from the right click menu to have the clip "rendered" using the "Offline" rendering algorithms which are far superior (but use more resources so can't be used in real time playback). There are multiple algorithms to choose from that can make the results of the render better based on the type of material being altered.
Sometimes the render doesn't eliminate all of the "artifacts" though (which is that warbling/weird arse noise you here). In that case you can go even deeper and open the Groove Clip in the Loop Constructor View and manually manipulate the transient markers to make it stretch better with less artifacts. That is kind of advanced though but worth reading up on.
Cheers.