Welcome to the confusing land of heating your DHW with a coal stove. There are a lot of variables. Things that seem to look good on paper turn out to be a waste of pipe and time.
I have a small Bucket a Day (BAD) coil fired water heater that supplies all our DHW. I piped it to thermosyphon to an old gas water heater that I pulled the burner out of. I am not using a pump. Cold water in goes to a T that I installed at the tank drain tap at the very bottom of the tank. Just up from that was another tap that I piped to the BAD inlet. The hot water from the BAD goes into a T that I put in the pressure relief tapping. Before someone goes nuts, yes I reinstalled the pressure relief valve in the T. The tank and the BAD are properly protected. The water out was piped as normal and the water inlet was capped.
If your feeding the inlet water directly into the line to the coil than it doesn't have enough time to heat up all the water that is being used. It sounds like your getting the water in the tank hot while it sits but on usage the inlet water is passing through the coil too fast thereby causing the wife scream sound that you hear.
If you can post a photo of your setup that will help. It's all a matter of getting the piping in the right spots. The trick is to use the hot water from the tank, not the outlet from the coil.
Hot water from tank = no wife scream sounds.
Hot water from coil = wife scream sounds