Hi, we get a clicking noise from two of our radiators when the heating
comes on/off. They are the largest radiators in our main bedroom and
living room. It's not a very loud noise but in the silence at 6:25 in
the morning it is really annoying!

As the other radiators are unaffected I assume it's not coming from the
boiler or air in the pipes. I've put lagging around the pipes in these
rooms where they touch joists etc and removed any air from the rads ,
all to no avail.

The central heating was only installed about 18 months ago and the
first winter we didn't notice the problem.
I suspect it may be caused by the radiator not having the plastic clip
where it is hung on the wall bracket and the expansion of the radiator
causes movement. The top half of the rad gets hot before the clicking
starts. The rads were removed for decorating etc last summer so the
clip may not have been replaced.

does this sound plausible before I get the plumber out to test this
theory?