Maybe I can share the experience I had during my first two WILDs.
Because I didn't even know I was doing it the first time untill I wrote it down the next morning.

During my first I was just lying in my bed, visualizing or daydreaming, whatever you want to call it.
But at a certain point I noticed I lost my connection with the real world, I felt I was in my visualization at that moment. I had done a WILD a never even noticed the transition.

My second one was more clear.
Once again I was picturing images in my mind but this time I did notice the shift.
I was imagining walking in a field looking at my surroundings and at one point I started running.
But at that moment I felt how I was loseing my connection to my body, it felt like I was being lifted up or something. It was important that I acknowledged this feeling but at the same time leave it in the back of my head and not pay to much attention to it.
In the end the floating feeling made it's way into my dream and I flew away.

So you see, WILDs can happen very naturally without much chaotic sounds and/or feelings.
The advice to focus on the mental aspects is spot on.

We know dreams are happening inside, so the inside is all that matters.