Random Inexplicable Freezes - where to start?

I've been out of this game for a few years. Forgive my rustiness, but I have a big problem I shouldn't be ignoring / coping with any longer. My system specs are up to date.

My custom build desktop from 2011 now, is having random freezes. There is no discernible pattern I can find, no hardware or software leads. I tried looking into the log a while ago, but couldn't find anything. ("Life's" been happening.) If there is sound playing, it will simply turn into a grinding-like brrrzzzz of whatever the last note of sound output was. There is no getting out of this freeze, and I have always had to just hit the reset case button. Gif's will freeze, the cursor won't budge, my spinning Avast icon freezes where it's at, the clock stops. But then no sign of anything abnormal in the log, other than not liking how it was shutdown/restarted. Admittedly, this has been going on for months. Sometimes it's good for a few days, sometimes I have barely been doing anything for a few minutes.

I know there is no quick fix or good enough clues in this, but I am finally ready to start tackling this problem. I'd like some ideas of where to even begin...

are you able to do ctrl+alt+del?

Not once it's frozen. Any other time it's perfectly normal.
It also isn't lagging down into a freeze, it's sudden, instant, and without any kind of warning.

perhaps download speccy and check your temps at freezing, here:
Speccy