Can you be a bit more specific with what you mean by "a strange sound"? That description isn't very helpful. Can you describe the sound you are hearing in more detail? Also, under what conditions (other than "turning up the volume") do you hear that sound? That is, do you hear it when you are playing any kind of music (such as a wav or mp3 file)... or do you only hear it when you are mixing with Studio One? Additionally, are there any particular frequencies that cause the "strange sound"?
I ask because I also am having a sound issue with my Eris 3.5 speakers. Whenever I play something with a definable 130.8 hz "C" note (such as the 3rd fret of the 5th string or the 8th fret of the 6th string), I get a heavy "rumble" or "booming" in the speakers. I've noticed if I play music from someone else (say from an mp3 file) that happens to hit that note, I get the same "booming".
Does the sound you hear resemble my description at all?
So far, I have not come up with a "solution", but only a "work around". That is, when I am editing my songs that hit that note, I use an equalizer to "tame" (lower the db) of that note a bit. That keeps the speakers from booming at the C note... That only helps with my own editing, however. It does nothing to tame that "boominess" if I am playing someone else's songs.
So please edit your request with greater detail on exactly what "strange sound" you are hearing and under what exact circumstances you hear the problem.
Here's a couple of more thoughts (and possibly a solution for you). Have you tried adjusting the two Acoustic Tuning Controls" on the back of the speakers? There is one for bass and one for treble... Perhaps adjusting the bass one up or down a few db might help in your case. Keep in mind these are "shelf filters", so adjusting them will not focus on just one specific frequency, but rather will affect all frequencies above or below your setting. Think of them as the bass and treble knobs (if you have them) on your car stereo. Playing with these might help tame the "strange sound" you are hearing.
Another idea (to help you isolate the problem) would be to reverse the Left and Right wiring of your speakers... If you reverse them, does the "strange sound" follow the wiring reversal? That is, if you were hearing the sound only in the left speaker, then reverse the wiring, does it then move to the right speaker? This would at least tell you if the problem is one of the speakers or the signals being fed into them.
Please let us know if any of this helps. Thanks.