There is a buzzing noise coming from my cello when I play, it just started recently. Does anyone know what might be causing it and what needs to be done to have it fixed?

Look Inside your F-holes and make sure your SOundpost has not fallen

It's still in place, I'm starting to think it's my D string. I haven't noticed the buzz on either the G or C and only occasionally on the A and the sound seems to be coming from the neck. Is my string somehow faulty?

Some cellos will come with little plastic things on the string to put where the string meets the bridge. A misplace one of those could cause buzzing. You might want to consider changing your strings if you havent done so within the past, .. year or so. Take it into a shop. They can analyze it, and if its an easy fix, it'll cost you little to nothing. If its a more hefty fix, then at least you'll know, huh.

i had that problem also, it was coming from a variety of things on my cello (i had a real cheap one: 4/4 $850) i had that little plastic thing, my pegs and fine tuners were loose and so was the screw on my bow,

so i got some better custome made pegs, better strings (2 larsens and 2 spirocores) , and a $550 bow. i also forgot to mention, if you have any wolf elimenators those may be loose and rattling

Many things could be the reason of a "buzzing" cello.
It could be unglued somewhere around the body of the cello or a crack which once had been repaired could be opening up. This has to be checked by a string instrument maker. In the winter, the air is dryer which shrinks the wood of the instruments and the change of temperature frequently unglue them. It is not expensive to repaire them.
The little screw at the botton of the end pin could also be loose.

The problem might be a wolf tone - usually around F or F# on the D string. It's sort of a buzzing/fuzzy sound. Difficult to describe. Try a wolf tone eliminator for the cheap option; or a new set up can fix it too for the more expensive option.

Hi, everyone
I had a same problem. I took avay the fine tunner from the string that made the buzzing sound. Everything is OK now.