Unless you have a very expensive hobby involving real diamonds, the only "diamond" I can think of here is the shape formed by rail tracks crossing each other. But why "smashing" and is the sound of a train crossing a diamond significantly different to that of one crossing points?
Language problem? The term "Diamond" is quite common here in the US to describe level rail crossings, though I've never heard of "smashing" a diamond. OP likely meant high speed effect and loud.
The cross-over structure is sometimes called a diamond junction or diamond crossing in reference to the diamond-shaped center. The two tracks need not necessarily be of the same gauge. A diamond crossing is also used as a component of a double junction, like the one illustrated on the right.
There are a few website that feature a ton of free sound effect noises. These can be configured into TRAINZ and activated by triggers. Go to the web page and run a search on the sound you are looking for and few examples might pop up if they have it.
If interested, I'll post a link.
