323001363 - S005 ENGINE HISSING

There is a low frequency noise coming from the engine whose intensity varies with the number of revs.
TEST RESULTS
1AIR INTAKE CIRCUIT CHECKALL OKPROBLEMS ENCOUNTEREDACTION
Check the condition and seal of the air intake systemMove on to Step 2Circuit component damaged.Replace the damaged component.
2ENGINE EXHAUST CHECKALL OKPROBLEMS ENCOUNTEREDACTION
Check the engine exhaust system, in particular:- Manifold- Pipe- Exhaust silencer- Catalytic converter front seal.End of diagnosis1. Pipe damaged.2. Rear silencer damaged3. Front gasket worn or damaged.1. Replace the pipe2. Replace the rear silencer    Op. 1076B20 REAR EXHAUST SILENCER - R + R 3. Replace the front gasket