Hissing Sound from Rear Axle When Car Is Unlocked After Sitting

[zonefive]

I just purchased an E70 with the third row, accordingly it has the air suspension.

Just had the rear diff replaced and mechanic needed to remove the left air bag from the suspension to do it.

Ever since, I notice if the car has sat for a while, there is a hissing sound when I unlock it. Lasts maybe 2-3 seconds, then stops. Is this normal? I never noticed it before the rear diff work, but only have had the car for a week.

The car doesn't sag at all. I'm wodering if the compressor is running to get the correct PSI into a leaking bag, maybe the one on the left which was removed and could have been damaged.

Any help is appreciated.

[Davidf]

Yep, I think your diagnosis is correct. The air compressor will activate upon opening a door for more than a few seconds. It could be your mechanic incorrectly reinstalled the air line or pinched it upon reassembly.

But, I think the compressor is activated by the rear suspension level sensor, not air pressure in the system.

[zonefive]

I don't have to open a door, just unlock the car -- does that mean that this may not be the compressor?

[pshovest]

My X5 w/o the air suspension does this......it's the fuel pump running momentarily to improve starting.

[seattle]

By the way, you may want to update your signature: "2012 E70 3.5 X-Drive Pre-Owned"

perhaps "2012 E70 xDrive 35i" or "2012 E70 xDrive 35d" ?

I bet you think the engine size is 3.5L

[zonefive]

Originally Posted by seattle

By the way, you may want to update your signature: "2012 E70 3.5 X-Drive Pre-Owned"

perhaps "2012 E70 xDrive 35i" or "2012 E70 xDrive 35d" ?

I bet you think the engine size is 3.5L

Fixed it, thanks. I was thinking it was the usual 3 liter and I couldn't figure out where the 35 came from.... also the engine cover makes it look like there's more than one turbocharger.