You might want to check your usage percentages with a simple sar monitoring (sar 1 100) to be sure that you don't go CPU bound and crash.
Possible you have a script (or application or other) that is spawning and respawning child processes. If you know a general time that this started, look through your cron and see if it started anything around that time.
Also check you disk space and see if it too is growing in a particular filesystem. If you do see something growing, you can use fsuser or lsof to see the user causing the growth and then trace that to the processes running.
You can use "monitor" to help determine what this "unknown" process(s) is. Remember, amateurs built the Ark, professionals built the Titanic.