Glad that my suggestion helped you with your bobbin winding woes.
It's important, actually critical that the bobbin holder be in position properly ... I just was not comfortable with it. One day the in-store mechanic sat with me and had me put it in and out numerous times, til I fully "got it". Now, I have no problems.
Just do some regular stitching without the AccuFeed in place ... that should give you a better idea as to how it sounds. There definitely is more noise with the AF than without. (Again, all comments from the 6600 perspective).