salsainglesa,

I seem to recall that this awkward-sounding beep was due to a ruby plugin. The plugin was calling the "UI.beep" function. I've searched, and found that's the case with the following plugins:

ContourMaker.rb
CutListAndMaterials.rb
Linetool.rb
Ldraw.rb
Multiwalltool.rb
PurgeAll.rb
SectionCutFace.rb
Slicer.rb
Slicer3.rb
Ultiwalltool.rb
VolumeCalculator.rb
ZVolume.rb

The culprit would have to have something to do with the layers (obviously,) but I haven't poked around in the above plugins to see if any of these access layers. All I can remember is that it had to do with an "older" plugin.

I did find the following discussion, but it's unclear whether the issue was resolved to the poster's satisfaction:
http://groups.google.com/group/SketchUp3d/browse_thread/thread/4317cbb9f84d77d8?hl=en

Perhaps someone else recalls the discussion to which I'm referring?

Taff