apt-get duplicate sources.list entry for google-chrome (Ubuntu 11.10)

I am running Ubuntu 11.10.

This is the only line in my /etc/apt/sources.list with the text "google" or "chrome" in it:

deb http://dl.google.com/linux/chrome/deb/ stable main

Sometimes (not always) when I run apt-get update, I get these warnings at the end of the output:

Reading package lists... Done
W: Duplicate sources.list entry http://dl.google.com/linux/chrome/deb/ stable/main amd64 Packages (/var/lib/apt/lists/dl.google.com_linux_chrome_deb_dists_stable_main_binary-amd64_Packages)
W: Duplicate sources.list entry http://dl.google.com/linux/chrome/deb/ stable/main i386 Packages (/var/lib/apt/lists/dl.google.com_linux_chrome_deb_dists_stable_main_binary-i386_Packages)
W: You may want to run apt-get update to correct these problems

If I run apt-get update again immediately after receiving these warnings, they don't show up the second time (or third time, etc...). But then the warnings always come back eventually.

In any case, installing/updating google-chrome works fine, but those warnings are annoying (and since I skim over them now, I may inadvertently miss some more important warning if one ever comes up).

Any way to get rid of these warnings permanently?