There are two common things that will cause this:
1.) Be absolutely sure that you are not running your cable modem through any extra splitters, and that you are on the lowest db ports possible. (Read my splitter section on configuring your splitters.)
If you have access to DC Taps, use them, they will most likely fix your problem in this case.
2.) If your upstream line is noisy, your cable modem provider will instruct your cable modem to raise it's upstream power in order to compensate for all the noise on the line. In this case, I suggest you review the Common cause for Fuzzy Pictures on Low Channels (2 through 7) section of my FAQ. It may seem unrelated, but Channel 2 and your cable modem return frequency are very close to each other.
If your upstream power is just "barely" too much, but runs fine, I wouldn't worry about it, but if it's so high that your cable company is threatening to take your kids away, then obviously you need to do something.
Maybe the line running to your cable modem is actually bad? Are you sharing it with a TV? Have a new line run.
Installing an AMP in this case will not fix the upstream power, it will just add another device the modem has to work through.
There ARE two way amps for situations like this. I do not know where you could find one, but I do know that they run in the hundreds of dollars range ($250 to $400).
Good luck with this one.
Note by habu187 : This is also caused by improper return path padding in amps and LEs or the return path at the node could wrong.
Feedback received on this FAQ entry: