Caldina Factory BOV vibrating?

[DanielA]

I have a 1998 Caldina GT-T. Recently I've noticed a vibrating sound that is coming from the large diameter section of the factory Blow off valve. It seems most prominent just above idle. I haven't noticed this vibrating before. Is this normal or should I look at getting a replacement.

I just had the clutch rebuilt and a bearing and seal kit for the gearbox so initially I thought they may not have screwed it back on properly but it appears ok.