I kind of see what you mean.
Here is the original triangle channel: http://benboldt.spymac.net/triangle2.mp3
And here it is by itself passed through the same filter: http://benboldt.spymac.net/triangle1.mp3
The original is poppy because the triangle wave doesn't always start where it ought to. It should always start right at zero, but often times it starts higher or lower than this producing a pop sound.
The filter I passed it through makes this pop more pronounced. While it should not damage your speakers (it is not an actual clip), I agree that it does sound bad.