Noise related to expansion of copper in Radiant / Hydronic / Baseboard heating

[rubadub]

Hi,

I'm curious if there are any experiences/insight beyond standard troubleshooting for this issue. The most practical resolutions i've seen so far are to straighten the fins (which i've done) and to ensure the return pipe is not resting on any metal hooks which could create noise... I do not have a return pipe that I can see in the entirety of the system, which I suppose means it's one long loop? I don't see visually that the pipe is impaired from expansion by any wall or opening and yet we still hear loud repeated knocking in various locations every time the pipes expand. It is different from the lighter popping of the fins expanding, which i'm relatively fine with since they are not as jarring as the knocking sound of these pipes... I've tried flushing the system but have realized that isn't the solution to this problem. I fear the problem areas are in the wall and unreachable unless I start tearing down the house to follow the entirety of the line... What are my options here?

 

[Diehard]

Yes, typically there is one or more loops, depending on the size of the house.
In many houses, you can see the lines drop down through the floor. So in those case can check to see that there is sufficient clearance for the pipes as they pass through the holes.
Hidden pipes is another story. Hopefully someone has some suggestions for you.