The Sigma 28-80mm zoom lens uses an internal motor to zoom and focus. As the lens ages, the gentle whirring sound of the motor may turn into more of a rattling sound. As long as the lens is still functioning, there's no need to worry about the noise. If the noise turns into loud clicks or the the lens ceases to zoom, take it in for repair or purchase a replacement lens.
Sigma is a third-party lens maker that is compatible with most major SLR cameras, such as Nikon, Canon and Sony. These lenses are typically cheaper than the camera-brand lenses, although sometimes this comes with a reduction in quality. If you notice a rattling sound inside your Sigma 28-80mm zoom lens, it could be normal motor noise or an expensive problem.
Lenses include many moving parts, some of which may rattle when you move the lens. These include ball bearings and stopdown levers -- when they aren't in use, they sit loosely inside their compartments. Shaking the lens may make them rattle. This should be a quiet rattle, and the lens should continue to work. If the noise is loud or the lens isn't working, the problem isn't the normal moving parts.
Many digital SLR cameras include a vibration reduction, or VR, feature. Some lenses incorporate VR technology as well to further reduce camera shake. If your Sigma lens isn't locked securely into place into your VR-enabled camera, the moving elements that reduce your lens' vibration may be moving independently. Remove your Sigma zoom lens and put it back on, making sure to line up the white dots and turn it until it fully locks in place.
Over time, the front cover of lenses may work loose, causing the lens to rattle. There are screws under the rubber focus ring that can be tightened to eliminate this rattle. This is likely an easy fix, although you should consider taking it into a camera repair shop to make sure the screws aren't overtightened.
If you hear loud, internal rattling every time you move the lens, it's likely an internal component has worked itself loose. It's important you take the lens in for repair immediately, as loose internal components may fall down to the glass on either side of the lens and scratch it, making the repair expensive. Get a quote before you have internal components replaced; it may be cheaper to buy a new lens.
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