Engine noise when dry

The spring (or let's call it a few warmer days) has finally came to Ireland and my sensitive ear started to notice rather quiet clicking noise from the engine. The noise gets faster (you'd get more clicks pers second) when the engine revs up.

It is not very obvious, the two mechanics I asked told me that they can't hear anything and instructed me to enjoy the sun - but I definitely can notice when the ICE starts or shuts down just by presence of this clicking noise.

What's strange, when it has been raining for some time I don't hear it anymore, the engine runs very smooth and quiet. It will keep quiet in the roofed parking garage too - so it is not the rain just masking the sound.

It does not matter if the ICE is hot or cold too.

I removed the serpentine belt and have run the engines for a moment without water pomp - but the sound is still there... The oil and filter has been recently changed too.

Apart from that the car runs fine. I get slightly below the typical fuel economy (5.9l/100km = 40mpg(us)) but I think it is still OK: I run only short distances (5-10 miles tops) and decided to ignore the pulse'n'glide technique as it kept my focus off the road.



Any ideas?

 

I've got it second hand, so I cannot be absolutely sure of the mileage - but it is 50k miles at the moment. At 45k miles when I got it, it still had the factory fitted tires (although very worn and I trashed them immediately) - so I am ready to believe that mileage.

The valve clearance crossed my mind - but I have excluded it. That was my line of thinking, correct me if I am talking rubbish:
- if clearance is the problem, then when cold the noise should be quiet as the oil is more viscous and get louder as the oil gets warmer;
- the mileage is low, even for the valve clearance check.

I was driving today to work and something else came into my mind: maybe the elastic exhaust join is slightly worn. The water allows it to seal and the engine is quiet - but when dry I can hear the additional noises getting out before the silencers... Sound theory?