Another Carb noise question

[A98Coupe]

Thanks for the suggestions guys. I'll try the wet/soapy rag test around the baseplate as Patrickt suggests and see if that points to the source. However, with my homemade engine scope, I couldn't detect any noise around the base plates of either carb. It was definitely coming from the front left hand secondary venturi - which is a mystery to me.

Bobcat - Thanks for the suggestion about the mixture screw - I'll try that but given that the noise is coming from the secondary venturi, the mixture screw only affects the primary fuel/air mixture right? Also, yes I do have a dual plane inlet manifold with 4 holes for each carb. This is why I changed the baseplate gaskets, thinking that this would cure the noise issue.

Rick - The carbs have only done 2000miles, so worn shaft bores is unlikely. Also, the throttle return spring is attched to the throttle linkage and not the carbs. I have tried wiggling the throttle shafts, but it makes no difference. I will try either WD40 or 30 wt oil on the shafts to see if that has any effect.

Thanks again guys - your comments are much appreciated - I will let you know what transpires.