My Holley does the same after I rebuilt it can’t figure out where it’s coming from exactly but it’s from within.
I would suspect the economizer diaphragm as that top already looked quite malformed (and the new diaphragm is a tad thinner). It does sound more internal though.
It runs much, much stronger since rebuilding and doesn’t seem bothered with it, so for now it’s good (and I’m swapping to a Carter anyway).
