new iPhone 4s model no - MC922LL has less strong vibrator then other models.

I noticed new iphone 4s has less strong vibrator motor on model MC922LL (att) bought through att store.

My other phone was brought from Apple Store which has a different model number. has more stronger vibrator motor.

Compared with 4 other couleges at work and its same accross all model no - MC922LL (its around 60-70% strength than other models)

Is anyone else have noticed same issue?