Thermal expansion? (Noise) (Ed.)

[DanAW]

Hi all, I hope you can help me.
A few months ago we started hearing a 'dripping' noise in our living room ceiling. Directly about the living room is our bedroom radiator - and so in the void between the two rooms are the copper pipes that lead to the radiator.

I called a plumber who told me (without doing any investigating) that it was just thermal expansion.

Reasons why I'm not convinced:
-I've had thermal expansion in pipes before and it always sounds more 'clunky' than this. This is very 'rythmical'.

Reasons why I'm inclined to believe him:
-There's no wet stains on the ceiling / no sign of water (although I've turned the rad off so potentially there's not enough water to stain).
-It only happens when the radiator is turned on / hot. Presumably if the pipe was leaking it'd drip all the time, not just when there's hot water running through them (as they're always full of water, right??).
-The boiler pressure hasn't dropped.

I know people will say "the leak will find you" - but my house has wooden joists and I'd hate to think that they're getting wet / rotting up there and I'm ignoring it.
That being said, we've recently had all new carpets laid upstairs so I'd prefer not to lift them up to investigate if it's likely I'm worrying over nothing.
Plus, why did I pay for a plumber if I wasn't going to listen to his advice?

Has anyone else experienced something similar?

 

[Burnerman]

If your boiler pressure hasn’t dropped I guess you have no need to worry. One bar when cold, rising to around 1.2 bar with heating on is about the norm.
Radiator brackets have a plastic slipper where they hook on to.....this can be left out, but a spray of silicone lube won’t do any harm.
It could also be your pipes are too tightly clipped, or they are trying to expand into an area which is too tight into a corner for example.
John