I agree with the previous post, because I had the same issue. The song I was working on would start making this weird sound and seconds later the program would freeze. When I looked at the performance monitor, the CPU was pegging. I wound up re-doing the song in another Music Production program because I needed to finish it, but I still needed to know what the issue was with S1.
In my case, I found my sample rate was set too high (2048). I lowered it to 1024 and the issue was gone. This might have been done when I upgraded from 4.0.xxxxx to 4.5.xxxxx. I also discovered that my CPU was getting warmer than it should have been. The thermal paste had dried out and was ineffective. I removed it, cleaned the heat sink and CPU thoroughly and applied fresh paste. I now have no such issues.
Also, it's VERY important to set autosave to a low value; I have mine set to 7 minutes. This way, I'll never lose more than 7 minutes of work!