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Thumping from dash when key turns on - any ideas?


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For about the last week, whenever I turn on the key in the Boxster (but before I start the engine), the right side of the dash will make about four soft thump sounds. I played with it this morning, and I could turn the key off, turn it on, four thumps, key off, key on, four thumps, etc. It didn't happen every time I turned the key on, but nearly every time.

I'm assuming this is some part of the HVAC system 9(like a valve) that is making this noise. Has anyone else ever had this issue? Is it an easy fix?

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Correct, it is in the HVAC system. Probably what you are hearing is the Blend Door Actuator or the vaccuum pressure building up in the lines pressing on the doors making them ready to direct air to the vents. You will hear this on most vehicles but it is louder on my Boxster than in most cars I've had.

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Correct, it is in the HVAC system. Probably what you are hearing is the Blend Door Actuator or the vaccuum pressure building up in the lines pressing on the doors making them ready to direct air to the vents. You will hear this on most vehicles but it is louder on my Boxster than in most cars I've had.

Anything to be concerned about, or should I just learn to live with it? Is there any way to minimize it?

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If it sounds like its coming from the far right side of the dash, its probably the fresh air/recirc flap actuator. The 986 uses electronic actuators to move the flaps in the evaporator housing - they aren't controlled by vacuum as in the previous cars. When these actuators get noisy they make the sound you're describing. It seems the most common one to make noise is the one for flap which opens or closes the evaporator housing to air coming in through the pollen filter.

If it bugs you, its possible to get just the actuator and replace it but man oh man get ready to drop some F bombs unless you want to remove the evaporator housing . You can see the bugger if you remove the foam from under the dash on the passenger side and then get on your back and look upwards. Its sandwiched between the body and the evaporator housing leaving you with absolutely no room to work. There is a 4 pin electrical plug and and 5.5 or 6mm screw holding it in. If you get this far you still have to remove the actuator from the flap which is a PITA to do without breaking the plastic arms.

In short, I would live with it. A dealer could probably take care of it for a few hours of labor - that is if anyone is willing to do it without removing the Evaporator housing.

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I wouldn't worry about it either. If it were engine, transmission, suspension I would definitely look deeper into it. At this point the noise is just a minor annoyance and I would drive it until it breaks. However, it may not ever break and repairing it (most likely at a huge expense) wouldn't guarantee it won't be back in the near future.

If anyone asks what the sound is, you could always just tell them it's the afterburner firing up! Then tell them how much safer you will be riding in your Boxster because you just filled up the red brake light fluid. :)

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