I might suspect a loose connection on your wiring but also you have to consider a faulty dimmer switch.Try to tighten the bulb on its receptacle and the lock screw of your dimmer if it has (Your breaker must turned off avoid you from an electric shock). If the problem still there I've advice you to buy a new dimmer switch to swap for a suspected one. If the problem still there then you need an electrician to isolate the trouble.

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