two things you say it only is noisy with the cover on? then something could be vibrating the cover. if not that check the gasket between the carb and your manifold I had a mismatched one and it acted like the reed on a clarinet as the engine sucked air in it would play an interesting tune.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.