I have a 1980 GMC straight truck with a GM 366 gas motor. Hits on every cylinder and will sit there and idle nicely. Has the typical dual exhaust with a muffler on each pipe. I did install new donut gaskets between the manifold and the exhaust pipe in 2013. The problem is it seems like you can hear exhaust, especially when the hood is open. Are the manifold to head exhaust gaskets blown out?????? I have owned a 283, 305's, a 327, and a few 350's but never had this problem. But, I seem to think when the head to manifold gasket is blown it will make sort of an exhaust ticking sound?????? Sounds sort of loud. Engine did have the air pump with the pipes into the manifold for pollution control. Has been taken off and the pipes were cut off at the exhaust manifold. I can't feel any air coming out of them. Maybe the exhaust manifolds are cracked??? Any ideas will help. Thanks.