20 minutes into the movie, Lisa comes over to Jeff's place for (and with) dinner. She is wearing bracelets to her left wrist.
The sound of these bracelets is loud in this scene. We can clearly hear it 2-3 times along the discussions.
Hitchcock does pay attention to a lot of details, and I wonder whether this was intentional, and to what effect. Image and sounds are usually quite minimal in his pictures, and these sounds may have some "cinematic value".
For the context (spoilers to a movie of the 50s), Lisa represents social life and elegance. She wears superb fashion, buys expensive bags, and shares top-society restaurant meals with the main character, Jeff, her male anti-thesis.
Lisa's looking flaunts elegance, and her calm voice and expressions seem very compatible with her looking. The sound of the bracelets may add volume to what she is supposed to represent, but that is just a guess at this point.