whining sound when accelerator pedal not pressed

[rennart]

hi, I wonder if anyone can suggest what is the problem please.
We have a R4 GTL running well. But, the last few days have noticed that when the engine has heated up,
there is a constant whining sound from engine area which occurs when the accelerator pedal is not pressed,
but car is running along.
The sound stops as soon as the accelerator is then activated, and then starts again when lifting foot of the pedal.

 

[André4Renaults]

It could be an air leak. When the throttle is opened the air flows through the carburettor and when closed a little air does flow through the carburettor but the engine produces a higher vacuum on over-run (throttle closed) than when under load, so if there are any small air leaks in and around the carburettor, they'll come to light when the throttle's closed. Also your explanation that the sound occurs when the engine's warm means that the leak is only noticeable when the metal warms and moves slightly.
I'd wait until the engine's warmed up and once the "noise" is there, spray WD40 around the carburettor and see if the noise disappears and/or the engine revs go up or down. If they do and the sound changes or vanishes, you have a small air leak. Try (GENTLY!) tightening up the carburettor to manifold bolts in the first instance and report back for more help, if needed!