Hi Stefan,

Welcome to the forum.

Do you have an engine shut down timer fitted, condenser fan or intercooler fan fitted?

Apart from the receive drier in the photo where are the other noises coming from? inside the vehicle? under the bonnet?

Does the A/C work?

Have you been playing in mud/water holes lately and had water inside the cab?

Apart from lights, is there anything else electrical that doesn't work? or stays on when the ignition is off.

The first thing I would do is make sure there is a good earth going from the negative of the battery to the inner guard.

It appears in your photo that the negative lead has been replaced and you may not have an earth lead going to the inner guard.

The other thing that can cause a feedback like you have described is a faulty alternator. If you can get it to play up every time , try disconnection the 2 pin connector from the back of the alternator.