Heating pipes banging against joists

I have a hydronic heating system in my home. The pipes knock in the walls when the boiler starts up. I've had 3 plumbers come verify that the boiler is working properly (valves not flowing the wrong way, enough space where the floorboard vent pipes come through). The house was just built shoddily without enough space between the pipes and joists. The knocking comes from a dozen places throughout the house, and you can follow the noise via the route of the water. It literally wakes the house up at night.
So I can rip apart the ceilings of each room and try and track each one down. Blah.
The last plumber we had suggested that we try changing the boiler to a new energy effiecient model that monitors the outside temperature and would not go from zero to 180 degrees when turned on. Instead, it would maintain a temperature throughout the system, only raising and lowering when needed, which would vary about 1-2 degrees. This would reduce the total expansion in the system, and thus reduce the knocking. I'm in Vancouver, so the temperature fluctuations are pretty small, anyway.
Logically, this makes sense. Has anyone seen this in practice, or have other opinions? And does ~12K for such a system sound about right?
mk
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Have you tried bleeding the air out of the system? Is the expansion tank working properly?
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I have a couple of spots in my house that make a little noise when the hot water flows. This is cause by expansion from the heated water. Do you have some visible sections that you can easily get to? if so, put an expansion loop in the long runs and you may get rid of most of the noise.
You need 4 elbows and a couple of short straight sections. Sucky ASCII are follows
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