m3 e36

[jmadrigal]

when i start my 99 m3 in the morning it the exhaust start to rumble for like 30 seconds then stops? is there a reason why it does this? also i hear a buzzing noise from the engine for like a minute

[gixerdave1983]

M3's have an air pump that directs hot exhaust gas from the manifold back into the airbox....thats what that rubber pipe going into the bottom of the airbox is if you ever wondered....its supposed to make the Catalytic converters warm up quicker. its belt driven and cuts in and out in exactly the same way an A/C compressor works so thats what the noise is. i think its a waste of time to be honest and the whole system just adds weight!

[TheTunerSource]

Yeah its normal. Happens all the time.