Internet speed slowdown

Using the Cox tool, I regularly check my download speed and it usually runs around 30 mbps. In the last couple of days it has dropped to 9.5 mbps or so. I have the Premier Package, a reasonably new (bought within the last year or so) Motorola SB5101U modem (DOCSIS 2.0) and am in Fairfax County, Va. Has my local Cox provider changed anything requiring DOCSIS 3.0, or are they just having problems?