How can I fix my Bissel Power Cleaner Bagless Upright Vaccum?

The motor on my Bissel Power Cleaner Bagless Upright, 2009 Model 92L39, is making a very loud reving sound, and is not picking up as well as it was. The three filters have been cleaned, the brush revolves and is clear of debris. It sounds like it's going to take off....what can I do? This was a Costco on-line purchase and still under warranty, but I would have to ship it back to CostCo for repair.

Thanks for your advice.

Terri