Brief sewer smell from bathroom sink (help!)

When I run the water on my bathroom sink for about 5 seconds, I get a fairly strong wiff of a foul odor, which only lasts a second or two. From then on, I don't smell anything. Some other information:
1. If I plug the drain, I don't get the smell. This points to the smell coming out of the drain, and not being in the water or coming out of the faucet.
2. The house is about 9 years old. It's a single sink. It drains quickly, without any slowdown. I've lived in the house for a year, and this only started a couple of weeks ago.
3. I've tried liquid drano, and a bottle of the foaming "pipe snake" stuff. Didn't make any difference.
4. This doesn't happen in the other bathrooms in the house, or any other sinks.
I'm pretty clueless about plumbing and home repair in general, so any tips would be appreciated. I haven't called a plumber yet, and I'd like to avoid it if possible.
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David Schroeder wrote:

Hold off on the plumber. The basin (most likely) has an overflow opening. This tiny opening is connected to the basin drain fitting by a channel cast into the basin. The channel gets loaded with soap scum which eventually supports a nice colony of mold. The mold produces odors. The sudden draining of the sink creates a puff of air which forces those odors out.
Use a turkey baster filled with bleach solution to inject fluid down the overflow. See if that cures the smell. It's not a permanent solution; the scum is very difficult to remove.
Jim
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Right you are! Everybody and his mother have tried to get rid of me but like a shit stain in your underware I just keep hanging on. HaHaHa.
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