Most likely, one of the valves has a loose washer. You would need to remove the handle, then likely remove a chrome cover, then there should be a large nut which will remove the stem. At the end of the stem there will probably be a rubber washer held on by a screw. This is the washer I'm talking about.
Since you've got the thing apart, now is the time to replace ALL washers, gaskets, and O-rings; also replace the screw that holds the washer on.
Any hardware store should have or be able to get the appropriate replacement parts.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.