I have an Aquaclear 70 that I bought brand new that keeps making a god awful buzzing sound. I thought it was picking up sand to I cleaned the impellor several times and even remove one of the extension tubes and it still buzzes off and on. So my question is there a fix for this or should I try to switch it out at Petsmart without a receipt? I have another 70 on the same tank and it doesn't buzz like this, it did when I first put the sand in but hasn't anymore. In a few months I'll be getting an FX5, so just need these to last a few months.