Here are some pictures of the space on the left mirror where the wind blows through and makes the whistling noise. With the tape in place there is no whistling noise at all. So far it has not prevented the mirror from folding and unfolding.
With the mirror in the normal position you can barely see the tape.
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With the mirror folded, you can see the black duck tape covering the chrome metal.
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View from under the mirror, folded.
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View from under the mirror, unfolded.
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