Right around the two-week mark on my AeroGarden unit, I noticed a huming sound. There is usually a very quiet hum coming from the reservoir, about as loud as a fish tank aerator pump, but this was a lot louder than that. A visit to the AeroGrow website suggested two solutions:
The first was to disassemble and clean the pump, and the second was that it was possible that I had a bad pump, and that they would have to send me a replacement unit. I cleaned the pump, and the humming didn't go away. While I had it open, I took a good look at it, and figured out what was causing the noise problem - it was a design flaw rather than a part failure, so while it looked as though it would continue to make noises, it didn't seem as though it was in any immediate danger of total failure.
Having eliminated the first option, I called the number on the company's website, told them about my problem, and they said they would send me a free replacement pump, no problem. The operator even gave me instructions on watering the plants in case the pump died completely before the replacement got here. Apparently, some number of AeroGarden units were affected by a bad batch of pumps, and they were replacing them as people called in about them.