Thank you for asking your question on JustAnswer. This engine is know to have leaking intake gaskets and will cause the noise your hearing. Usually as the engine warms up the intake will swell and the leak will reseal its self and the noise goes away. The fix in most case is to replace the upper and lower intake gaskets.
First verify if there are any vacuum leaks, use carburetor spray or propane around intake area while monitoring short fuel trims, if major drop in fuel trims while spraying carburetor spray or propane, suspect there is still a vacuum leak.