Whistling TRV

[kofi2003uk]

hi,
i have one radiator with TRV that starts to kind of whistle after about 2-3 hours when heating is turned on . if i turn the trv either way it stops . but the noise starts again when it stays on for a while (could be an hour to say 2hours then noise starts).

i checked the valve pin and its not stuck. i pushed it down and up a few times with no resistance. i unseated the TRV and reseated. the issue is still there. anything i can do to stop this noise or is this a case of replacing the TRV/valve. thank you

 

[Exedon]

Whilst current trv's are bi directional occasionally you get one that's noisy when closing.
I'd be betting it's on return side of rad.
Just change it and move on.