Noisy Aquaclear 200

Try turning it off and on several times. The impeller may not be seating right. The plastic lid may not be on all the way.... There may be something "in" with the impeller??
 
I agree, try taking out your impeller, cleaning it then reseating it. If the noise continues, try either removing the lid or putting a small weight on top of the lid.

I was occasionally getting some vibration noise from my Aquaclear and got rid of it by replacing the lid with plasticwrap.
 
I have a aquaclear mini and it was kind of noisy. My brotehr told me to put more water in the tank. It worked really good for me.
 
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