I am having a weird rattling sound coming from the passenger side of the engine - where the timing belt is. It happens only when the engine is cold and disappears almost completely when it warms up.
It is noticeable at idle and low RPMs (it gets louder when I pump slightly the acceleration pedal). I tried removing the accessory belt - the noise is still there, so it is not the AC, alternator or power steering. Also I replaced the timing belt and all it's components, EXCEPT the water pump recently (~20k miles ago). The car has ~125k miles currently.
That rattling started recently - maybe in the last 5-6k miles.
It sounds like there is something is loose and rattles - metal rattling sound. It is difficult to say where it is coming from, but my guess is from the crankshaft pulley area.
Also I recently removed the Timing belt cover to inspect the TB tensioner and the idle pulley for vibrations, but they were fine. Any idea? I believe it is getting louder and louder in the the last few months. I am out of ideas already. Thanks for any help.

 

Some update: I still have this sound on my Volvo, and I was able to record it:
https://dl.dropboxusercontent.com/u/...ling_sound.mp3

At some point I started thinking if this could be the water pump? As far as I know if there is a noise from the water pump, it would be constant and would not change when the engine warms up, and it wont be rattling.
Again, I removed the accessory belt (no alternator, PS pump, AC compressor involved), and the sound was still there.

Hope anyone has an idea what could that be.

 

Good sound recording of the problem.
That does not sound good at all.
One gets the impression of water pump impellor blades just touching the housing somewhere when spinning.
Once the operating temperature builds the looseness in the pump bearing may reduce with expansion, hence it sounding ok after a while running.