Hum - solved!

[Jim Haseltine]

Had my car idling with the bonnet open this afternoon and noticed a noise I've never heard before - a hum towards the back of the right side of the engine which seems to be coming from somewhere below and behind the PCV. Haven't had a chance to get a stethoscope in there yet but I'm thinking it's either the turbo (which will be a pain as thanks to badly timed retirement and lockdowns it's not done much since I rebuilt it) or the vacuum pump.
Ignoring the possibility of the turbo, has anybody else noticed any noise from the vacuum pump? Can't hear the noise inside the car so can't tell if it changes with revs.

[IanH755]

You get a quiet yet distinct vacuum cleaner/hair-dryer type sound from the rear of the engine on the drivers side during a cold start (upto 2 mins) which is caused by the the secondary air pump system.

There's the potential for this pump to remain activated after the cold start if it becomes faulty.

[Jim Haseltine]

I've heard that - it's quite loud, in fact my other half has remarked on the car sounding 'like a jet' when I've started it, so I don't think it's that although it was my first thought so I'm not discounting it. This is quieter, an almost subsonic hum but loud enough to hear with the bonnet open. I'll dig around later when(if) it's stopped snowing.

[Jim Haseltine]

Yesterday was written off because of snow and later rain which continued for most of today so it wasn't until after dark that I managed to do anything much outside. With the bonnet closed the hum can just about be heard. Under the wheel arch it sounds to be rearwards of the drive shaft and strut which sort of suggests that it's the vacuum pump but cars are great ventriloquists so I'll need to dig further.
While I was about things I ran a code scan which threw up a fault with the J197 level sensor that had me scratching my head. Took about an hour before the penny dropped (at least I hope so) - the car is on stands so the suspension is at full travel. I'm doing nothing about it unless the fault returns when the car is back on it's wheels.

[Jim Haseltine]

Really noisy now and it sounds like it's the turbo which means I'll probably have to pull the engine again. To cap things, not only has the battery gone flat again but my daughter misjudged reversing into the drive tonight, clipped a cracked wall pillar which dropped and on the way down clipped the far left edge of the RS front bumper just in front of the wheel arch. So that'll have to come off to be welded and resprayed and once the weather improves I'll have to get a brickie in to rebuild the wall. They say things come in threes - I had all of them within about half an hour.

[Fatneck73]

Wow Jim...fingers crossed you are right and the bad luck is over.

[Jim Haseltine]

Looking on the bright side of things, the damage to the bumper (now plastic welded, filled, sprayed and waiting to be compounded) has given me an excuse to deal with other things on the car - like the RH headlight which has been filling with condensation for months. While I was under the car having just removed the engine panel I took off the intercooler hoses to find them dry - the first time since I've owned the car (coming up on 5 years) that there's been no oil in them, so I guess my efforts rebuilding the turbos worked at one end of them at least.
Next task is to take a look at what's involved in getting the downpipes off with the engine in place this time but that's not happening in these arctic temperatures.

[Jim Haseltine]

At long last the source of the hum has been traced. With the car having been off road (apart from a few short but technically illegal test drives) for best part of two years I took it to my Steve for a MoT today - which it passed although the emissions were borderline. While there we had a good hunt around the right side of the engine compartment and pinned down the noise to the cyclone in the oil tank. I'd never heard the noise before taking the car off the road but considering all the issues I discovered with the lubrication system (both turbos hemorrhaging oil at each end, the shaft seal doing the same, a faulty PCV unit and two of the three non-return valves failed open) I wouldn't be surprised if system has never worked properly in all the time I've owned the car. It's still smoking a little from the tail pipes at idle after a run but that again is no surprise considering the amount of oil that leaked from the exhaust when I had it off the car.
The best thing though is actually being able to drive the car legally once more.
Now I can concentrate on sorting some minor paint and trim issues.

[ruedisrs6]

I had the same noise and it appeared after an engine-out repair. I narrowed it down as a vibration that basically originated from the oil module, was transmitted via the oil tube mounted to the front of the oil module and was amplified by the catch tank serving as a loudspeaker. The repair Shop changed the cyclone on top of the oil tank, but this did not change anything. Was most prominent at 1.800 -2.000 rpm. Went away after a couple of 100kms and an oil change. Never appeared again. My PCV and non-returned valves were checked to be ok.

[Jim Haseltine]

The hum has faded to a point where it's hardly noticeable now. Unfortunately after most of the month with on/off use without smoke the car is now once more guffing out a cloud of smoke when started. On Saturday evening I started it for the first time in a couple of days and it took about a mile for the exhaust to stop smoking then yesterday morning (after it had been parked up for 9-10 hours) there was a similar but less long lived cloud.

[trj]

Hi Jim,
I`ve just posted a thread with the same issue.
I have my sound only after start up with warm engine.
If I put in drive, the sound stops. If I do nothing it stops after a few sec. It`s very low nois, not hearable from inside the car with closed doors.
Have you fixed your problem?

Regards/Robban

[Jim Haseltine]

The hum (or whatever it could be called) has gone - or at least it's faded to the point where it's not noticeable. The only work done to the engine since this time last year that could have had an impact on it was the replacement of a number of non-return valves in the breathers. It rarely smokes now (maybe once in a couple of weeks) and then only a small cloud on start up. It still pours oil out into the intercooler hoses though.

[Jim Haseltine]

That was tempting fate, especially close to MoT time. On Sunday it blew a cloud of blue smoke on start up and then again yesterday.