Why does a breaker buzz when you turn it on?
CEB Ltd. is a now obsolete panel mfr., but they used Cutler Hammer circuit breakers. You can still buy those breakers from Eaton (the new name for Cutler Hammer) and they still use the same part numbers.

Those are "bolt-on" circuit breakers, meaning the way they connect to the panel bus bars is a bolt (screw) instead of a stab-in arrangement. Bolt-on breakers are mostly used in industry, not residential because industrial and commercial users are usually moving and modifying circuits more often, so plug-in breakers get loose and sloppy over time. The down side to bolt-on breakers though is that the connections must be periodically tightened, something that an industrial user would have as part of a routine maintenance program. Most homeowners however are unaware of this need, hence the preference for stab-in breakers.

The point is, the buzzing sound is often a sign of that bolted connection getting loose, and it is VERY dangerous as it could eventually start a fire! If you are uncomfortable with messing with the guts of your panel, hire an electrician immediately. They (or you) must remove that breaker and clean off all mating surfaces on the breaker tang and the bus bars before re-assembling it. DO NOT just tighten up the screw as there is likely debris in there now from arcing that has been taking place.