Pilot 2003 diesel - Start problem - click noise at ignition

A new episode in the van refusing to start.

After the glow plugs hypothesis this winter.

When I turn the ignition on, nothing happens else than a click noise (followed by a kind of spring resonating noise)

the battery is charged (I did it with a charger and my friend helped me try to start by connecting his running van engine)

I noticed a loud hissing noise the last time I used the van (louder than usual at the start)
This day was really hot (hottest day of the year in UK)
Next days was heavy rain (my Pilot doesn't like rain - it sometimes refuses to start when it s too wet but usually is fine once dried up)
2 or 3 days later the van wouldn t start.

***
So I checked the Earth today with a lead cable from negative to engine. It didn't start. Meaning it's not the Earth if I understood correctly.
I also found this video online, it's a very clear explanation about starter motor troubleshooting.
 That can be handy too from good ol' Star Scotty Kilmer:
That's a potential solution:

Hows is the starter wired up to the ignition?
There is a solenoid on the top of the motor. This is wired to the Start position on the key (thin wire with spade type connector). When the solenoid is energised, this not only brings the motor pinion into mesh with the ring gear on the flywheel but also connects the motor's windings direct to the battery via the thick cable fixed to the motor with a nut. The battery supplies suffucient "kick" to start the engine then, when the key is released, the solenoid is de-energised, the pinion retracts and the motor windings are disconnected from the battery until you next need to start. ******

This is a LDV Pilot 1.9D (1996-2005) starter motor manufactured by Universal Rotating Electrics. A modern starter motor works when current from the battery is applied to the solenoid, when you turn the ignition key. This then pushes out the drive pinion to mesh with the flywheel ring gear and thereby turn the engine.

***

I cleaned up the earth of my battery and I tapped lightly on the starter motor with a hammer on a stick. The van started up! I ran the engine, went around, everything was working fine. Left it parked one night. It rained the next day and at night I started it up to go to the petrol station. Once there the starter got stuck again. Tapping did nothing. I had to push the van to start the engine. Lucky me someone helped out. Now i am looking into that: