Yes, itīs normal. In my car, when the r.p.m are high, and I put the throttle off quickly, the exhaust shoots a bang! like the bang-bang in a world rally championship car. Itīs very useful when other car is too much near in the highway
Check the gasket between the exhaust manifold and the turbo. If this gasket isnīt perfect, this is the problem.
Greetings.
Julian
1987 Alfa 75 1.8 Turbo Evoluzione
1988 Alfa 75 1.8 Turbo America