That trickling sound you hear in the bathroom could be a leaky toilet wasting 50 gallons of water a day or more. But sometimes it leaks silently. Wait about 8-9 minutes. Inspect the toilet bowl for signs of blue dye indicating a leak. If the dye has appeared in the bowl, your flapper or flush valve may need to be replaced.
Parts are inexpensive and fairly easy to replace.
If no dye has appeared in the 8 to 9 minutes time, you probably don't have a leak.