The IC engine (3) is acoustically isolated from the passenger compartment (1) of the vehicle in the engine compartment (2). The air intake for the engine is fitted with an air filter (4) which takes in raw air at the front of the engine compartment an delivers filtered air to the engine. An additional hose (10) connects the air filter acoustically to the engine compartment. This enables the driver to determine the state of the engine. The additional hose incorporates a membrane (11) to prevent a direct air flow to the passenger compartment. The two sections of hose have a resonant frequency of about 2oo Hz and connected to an intermediate hose section (12) which holds the membrane.
