Hissing from front end when at low revs

[mini-kerm]

I have a 2005 Cooper and it's recently been in for the sump and rocker cover gaskets changing under warranty as it was leaking tiny amounts of oil.

Since it's been in for this work i've been able to hear a quiet hissing when the car is idling and in the lower rev range, it goes away after about 3k revs and then totally disappears after 15 minutes of driving.

Now am I worrying for no reason and its just a coincidence thing because of cold weather, or could it be something else?

[Minimalistix]

It's obvious that your car is leaking something and it's not a big deal if you didn't feel anything while driving. I'll go for diagnose check if the engine management detect a problem about it. Most probably there is a little mistake on installing your parts. Get it fixed tho :P Drive your car perfectly

[Lucky Dave]

Im would think its a intercooler boot leak following the rocker cover gasket change.

[mini-kerm]

Blimey sounds more serious than what it went in for in the first place!! You dont expect mistakes like that from a BMW service centre! Will phone them up first thing Monday.

What exactly is an intercooler boot?

[r1_kde]

Well if you have a cooper and not a coopers S you don't have them.

The go between the intercooler and the horns.

Where does the sound come from? it could be your exhaust blowing slightly around the cylinder head and when it gets warm it seals, or it could be on the plenum side (inlet manifold)

[Lucky Dave]

whoops yes! too much fast reading!

[mini-kerm]

It is a 2005 Cooper

It comes from the left side of the engine (as you look from the front)

It's like a whoosh whoosh whoosh noise at first then becomes a hiss when revving, and then disappears after 20mins ish of driving

[r1_kde]

it could be your oil pump/water pump and though theres no fault you are listening to the engine as you have had work done. Personally I would get it checked out just in case.

[C.Noble]

My best guess would be that they have forgotten to reconnect one of the EVAP purge solenoid pipes, a little black plastic valve above the alternator that should have a pipe going in the top and bottom of it.

Or one of the two breather hoses going into the rocker cover.

Please tell us what they found when you get it fixed, thanks.

[mini-kerm]

Will do, thanks for your help guys. It's booked in for next Wednesday so will let you know after then.

Hope they don't try and fob me off and charge me for something! Is there any way of me checking if it could be something not connected? What to look for etc before I take it in?

[mini-kerm]

Well they've fitted a new aux belt (is this the same as air con belt?) they thought it might be the water pump as one of you said but checked the aux belt first and thankfully it was that.

Will see if the whistling has gone away when I drive it home later...