You don't say what type of bar and stem you have on there but sudden new bar and stem noises should not be ignored. The fact that water silences it may be a clue that there's something happening between the bar and stem, where the stem clamps the bar. Remove the bar and have a look for rouge. This will be black wear marks. Aluminium fragments immediately turn black when oxidized and breaking loose, leaving a telltale clue as to where there is movement between two parts. It may be that the bolt is about to fail and its tension is thus no longer what it used to be. Check the bolt/s carefully for a crack where the first thread on the bolt-head side starts. It wont crack deeper in, just at the first thread. If that looks OK, re-assemble and torque properly. But first inspect the bar and see if it is still perfectly straight and symmetrical on the left and right of the stem clamp area. If fatigue has set in, it will show up there.
Some sort of lubricant is not the solution. It will only mask the problem.
