It's funny that you brought this up as I'm having the exact same issue. They replaced one of my 2 water heaters and a water circulation pump just before I bought my house. A couple of months later, I had the second water heater replaced under warranty. I still have water dribbling out on the floor so I put some catch pans under the various heaters and vent pipes to see what, exactly, was still leaking...

Turns out it was the pressure relief valve on the #1 water heater. Did a little reading and am convinced that I need one of those expansion tanks to moderate the pressure spikes. It's on my list of things to do, too. Gotta sit and think about the logic of the system to figure out where it should be placed based on how the 2 water heaters are plumbed to the water system.

Fun times as a homeowner.