Re: Exhaust sound coming from smog pump, normal?
The pump that is sitting by the firewall is an air injection pump which pumps fresh air into the exhaust manifold at times when the engine is still cold, leaning out the exhaust gases by helping the cat run a "second burn" of the exhaust. If it is this pump then you should check the Vacuum Control Valve [P/N 11 72 1 744 255]located just off of the exhaust manifold. It's where the hose from the air pump runs to.
Hope this helps.