I hear a pinging sound when I do bends, what is wrong?
If you hear a "pinging" sound when you bend the plain strings, the most likely cause is that the 0-fret has become dented/deformed from the string resting on it, or from accidentally hitting for example a wall or other solid object. When you bend a note, the edges of the deformation causes the pinging noise when the string is pushed across it. This is natural, and can occur over time - there is no saying how quickly it will appear, if ever. Sometimes these dents are so small that they are not readily visible to the eye, and can even occur during shipping, although these are exceptional cases.
It is also (generally) easy to correct by removing the strings and polishing out the small dent in the fret with 400 grit wet sanding paper (remember to mask the fretboard first with high quality masking tape). When the deformation has been polished out, follow up with 0000 steel wool to get the fret back up to a nice gloss.
Eventually, the 0-fret will be worn to the point where it is lower than the remaining frets, which causes buzz when playing the open strings. At this point, it is time to replace it, which only a skilled technician can do.
More rarely, the cause of the pinging noise is at the bridge end, caused by a burr from machining the bridge saddles. The fix is the same as above - polish it out with 400 grit wet sanding paper.