Very slight noise that can be heard inside the cabin. I think it resembles the sound of a bearing. What could it possibly be?

I have a Peugeot 406 Petrol (1.8 16V Engine).

When I sit in the car with the engine idling, I can barely hear a noise that I’m not sure where it is coming from.

I think it is similar to a bearing noise but I’m not sure. I opened the hood and listened carefully with a rubber hose (one end into my ear, the other end near any part that I suspect could be the culprit).

I checked alternator, idler pulleys, Belt tensioner, AC Compressor, Hydraulic pump and all around the engine but I didn’t hear anything that sounds abnormally.

I thought maybe it comes from the gearbox but when I fully pressed the clutch (to prevent inner gearbox shafts from spinning), it made no difference.

The only thing that I can’t inspect is the water pump bearing because it is inside timing cover and I don’t have easy access to it.

What do you think about the noise?