Does not mean there is not a problem with the Internet connection. If the ping plots look good, then it could be a million other things software related.
Heck, it could be an installation of some application that replaced a system file causing it.
The only interaction with your modem connection is over at the first hop of your ISP. After that it is all Internet TCP/UDP packets.
It could be the phone company causing it as well. If your modem decides to retrain, it will cause a disco. Modems can do this several times, depending on the quality of the line connection.
This one is actually easy to test. Cap your modem connection spped to 33.6K. This changes the protocol of the physical connection and should reduce/eliminate retrains.