OK, so I think I know now, at least a bit, what is causing the most "interference" or "overdrive" or whatever it is. I'm not that knowledgeable about that kind of stuff. Anyway, so it seems to be sine waves that causes it. And waves that are almost sine ways(just a little bit different). But I like that kind of sound...maybe it's better to mix both my samples I've made and samples other people have made? Yeah...
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Also there was something I read here:
http://www.milkytracker.org/docs/Vhiiula-TechniquesOfChipping.txt, that made me to call it "interference".
Quoting "You should use as many different chipwaves as possible in your chiptune. This is because the same chipwave, played at different pitches at the same time, will naturally interfere with itself and cause unwanted side effects."
I think it's the same thing, though I haven't really seen it much with the other waves, just sine waves...