C280 M104 engine pump noise??

[unkl300d]

Hello All, just did the archive search and did not find relevant info.
My 1995 C280 with the M104 6 cylinder engine has developed a mild noise, apparently after the engine is warmed up.

Using a stethoscope, I was able to pin point the sound as coming from the driver side body of the water pump.
(last replaced Dec 2011 or about 8K miles ago)

The sound is similar to a metal object bouncing around inside the pump.

I can't tell whether the sound is resonating from some other internal engine area but so far it seems isolated to the water pump body.

Is this the sound of the pump bearing going bad?
Can it be something inside the engine behind the pump? Like what?

No water leaks (yet) and no over heating.

When cool, or cold, there is no noise.
Noise is muted and not sharp but audible inside the cabin driver side at idle when engine is hot.(not a sharp noise like a diesel engine 'nailing' noise)

Any tips from C280 owners or knowledgeable Mercedes savvy members?

Thanks !!