I have to agree with Homebound, under the general heading of "the toilet still leaks" there are a number of possibilities. You stated that you changed the flapper and the flush valve so I am assuming that you mean the water level in the tank is slowly dropping and causing the fill valve to repeatedly open momentarily. If you changed the flush valve a new flapper should have come with the flush valve kit, so for the moment we can rule out the possibility that you have the wrong flapper. There was a time when the flappers were all the same and we just carried a box of "Corky's" on the service truck, but with the advent of low-flow toilets they had to slightly redesign the flappers and flappers are now rated by the GPF (gallons per flush). (They now make universal flappers that have a rigid plastic mount and the rubber ball can be rotated on the mount to adjust for the GPF) There are primarily two different methods of mounting the flappers. Most flappers have two arms that extend to the standpipe and there are holes in the end of the arms on the flapper that fit over cast plastic fingers extending off either side of the standpipe. Check the holes in the rubber arms on the flapper to make sure there is no excess rubber in the holes that might prevent the flapper from freely swinging on the fingers, then check the plastic fingers to make sure there is no excess "mold Sprue" plastic on the fingers that would interfere with free movement of the flapper. There is a style of flapper mount where there is no fingers on the standpipe. Instead the flapper has a molded rubber ring that fits around the standpipe. This type of mount can be a real PITA to adjust because if it is even slightly too high it keeps the back of the flapper elevated above the flush valve seat, and if it is slightly too low it puts a downward force on the back of the flapper which causes the front of the flapper to be raised slightly. Personally i try to avoid that type like the plague. Lift the flapper and run your finger nail around the top mating surface of the flush valve. If you feel any slight bumps use a piece of 600grit emery paper to smooth off the seating area. Check the length of the flapper lift chain from the flush handle. Properly there should be 2 links of slack in the chain. (The flush handle lift arm should be able to move about 1/4 to 3/8" before it begins lifting the flapper.) If the chain is too tight it can hold the front lip of the flapper above the flush valve seat. If the chain is too long it will produce a sluggish flushing action. Check the tank water level. In the inside wall of the tank you will find a "Water Level" index mark either painted on the tank wall or perhaps embossed into the ceramic casting of the tank. If the water level is too high or too low adjust the flush valve float. (The index should be about 2" below the top of the standpipe.) Check the trap primer line, which is the small diameter plastic line that runs from the fill valve to the top of the standpipe. Make sure that the line is positioned so that it cannot interfere with the free movement of the flush handle chain. At this point you have covered all the common problems associated with water leaking from the tank to bowl and causing the fill valve to repeatedly cycle. If this has not resolved your problem please give us more detailed information about the type of leak your having and we can offer additional information.

Yes, worry.....until you find out what it is. It may be something that can be safely ignored or may be a problem that needs attention. Never ignore suspicions of leaking until you know for sure what it is. Personally, my hearing isn't good. I've often asked someone with good ears to help me locate and identify sounds that are otherwise mysterious to me. In any event, I never leave dripping sounds alone until I know what they are.

Flush valve is the part that flapper attach's to and tank must be removed from bowl to replace it. Ballcock is the part that float attach's to and refills tank after each flush. Which did you replace?

What the OP is describing sounds like he's talking about the tank to base connection. Does the leak happen when the toilet is flushed - or does it happen when the water is in the tank and not flushed? Water can drip down the tank bolts, but be originating from other locations such as the gasket where the flapper mechanism goes through the tank or the gasket between the base and the tank (this would happen when it's flushed). Also a possibility is that there's a hairline crack in the tank.