Hi Chony
There are two main types of fittings, one which uses a choke & starter, and one which uses a ballast, so is starter less. (Also known as instant start)
These days the cheaper fittings tend to use starters, whereas office specification use high frequency ballasts.
If it is buzzing you can try fixing the light fitting more secure, and making sure there are no loose heat shields in the fitting, if both fail then you will need a new fitting.
Go for office computer spec, but be warned they are expensive.
Hope this helps.

Bill