Looks like my iPhone vibrates a little bit faster than supposed

Hello guys, I recently bought an iPhone 4 used from US and I noticed that it vibrates in a strange way, it really looks like it vibrates with more "strength" than the normal, I have compared to another iPhone and even the sound looks different, it looks like it's faster or something. I tried to use another vibrator from other iPhone but still did the same.

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Please? Anyone?

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bump........

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Did you compare it with another iPhone 4, and were they both purchased around the same time? Phones will often vibrate with more strength when new.

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