Strange but true.

CTM - silicon, or silicone?  There's a difference I believe.

I believe the squeak is caused by the shape of the sand and the air pockets around them, is that right?

I think it might actually be silica, I just did a google and seen this 

Squeaky Beach, so named because of the sounds you'll hear while walking along the sand. The Parks Victoria's expert explains that 'the rounded grains of quartz make a squeakingsound when you walk, giving this popular local beach its name'.20 Aib 2017

[img=16x16]data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAABNElEQVQ4jY2T0VHDMAyGv3AMUCawe2aAbNB2AtoJKBvQCbhOAJ2gMEGzAWEC2vf6Km+QDcyL3VNMyOEnSf5//ZIsE2MkxsjYccY+O2Mnyj9k3s0fhHUmOGNr4EXd7YFl9qusXlVVBljgAkyBLtmtD7Jyxq6BPcBZLhUwWMEBaHwQSeAJcEqJXxOmzeBegqRQA1/O2LkqtU3kPIdj5twW6rlXAzwUd0tln7JxncG9ndbANyBJSat1wFwluDvLpStbmCfgAtipeF2QGx+ky45OMAN2aXizFBPgrWjlQzvlK2RwVtzQ7118kEYTrkP0QVZwXRyAJlVgFX5bCA7uQZ2IT/R7P/og7/9J8Ahs06BmKr4ZwP7aA3yQhXLzU259kHYoAWO/0RkbnbGfY7zB36jOEViNAX4A9Rt0Cyk15YcAAAAASUVORK5CYII=[/img]
Squeaky Beach, Victoria: Unknown wonders' of Australia - SBS


I also found this you tube for one of the beaches on the gold coast where we visited.

https://m.youtube.com/watch?v=kSEYgWegbys

Have a listen it’s fascinating