I have recently replaced everything in the toilet tank and now every 3-4 flushes I hear a trickle of water - not on every flush. I don't know what else to do help!

If you don't have a leak, it may be the flapper, after flushing and flapper drops see if applying a little pressure on the handle helps seat it, if you do this a couple of times and don't hear it, may have just been the flapper.
Couple of good plumbers here may have good accurate info on the filler.

I have replaced the flapper and the seal looks good to me. Anything else it could be?

Tonight put some food coloring in the tank, Next morning check the bowl. It should be clear with no color. If you see color you have a flapper or flush valve leak. Let me know what you find. Tom