I have a new and interesting noise on my car.

It's developed a whistling noise that changes with RPM. It sounds like it's central, somewhere behind the dash and quite high up - perhaps near the windscreen.

It's not related to the air vents as it still happens with them set to the lowest speed/off.

If I prod the throttle and the gearbox kicks down the noise gets louder as the RPM jumps up. If I slowly increase engine speed the noise slowly increases as well.

It doesn't seem like wind noise as it's most noticeable at low speeds (before being drowned out by wind noise at higher speeds).

I can try to get a video later.

Air leak in the intake? Mines a Thor and given where I think the noise is I'm wondering if the "bunch of bananas" has cracked somehow.

Is this something that has been known to happen?

Vac. line from cc to brake pedal switch? They tend to chafe where they enter the bulkhead or split at the switch itself.

That sounds easy enough to check - I'll just see if the CC works on the way home.

The main engine/radiator thermo-viscous cooling fan seized up? I noticed it seemed to be going that way on one of the P38s I recently converted...

A whistling noise from a vac leak would get quieter with decreasing manifold vacuum / increasing engine load (quieter when you put your foot down).

Cruise control appears to work perfectly fine, so unlikely to be that.

Lpgc wrote:

The main engine/radiator thermo-viscous cooling fan seized up? I noticed it seemed to be going that way on one of the P38s I recently converted...

Not mine was it?

Planned to get a video of it this morning but it's stopped. Typical, it was doing it all weekend while I was away and on the way to work yesterday but nothing now that I want to look in it!

RutlandRover wrote:

Not mine was it?

Might well have been, I haven't converted loads of P38s lately, yours was one I converted.

Edit - Mind you I'd look a t*** if having just said TV fan it turned out to be the LPG reducer whistling! Make sure it doesn't only happen when running on LPG.

If the viscous is seized it isn't a whistling, it sounds like you have a jet engine under the bonnet. You should notice it when you start the car after it has been standing, there's a roar as you rev it which goes away after a few seconds of running as the viscous frees off (unless it's bloody hot and you need it).

Totally agree with Gilbert.
The one I noticed wasn't fully seized but seemed to be 'going that way', overly grabby. Weather was cooler then but did it from cold.

Whistling/whining? Another thing might be the alternator.

Have you listened around the engine bay?

Got to say/agree I can't really see you mistaking a 'whistling' around the dash with a TV fan or alternator noise. Ferryman's vac line scenario seems to fit the symptoms the most.

Depends on the year..

Won't be cruise control as that doesn't use manifold vacuum , it has its own vac pump for that.

If it's a Thor, then alternator bearings are known to whine, I don't think I've heard one yet that doesn't at least whine a bit.

Also known issues on tensioner bearings, and also the idler pulley a on the front of the engine.

Does it do it with vehicle stopped/ in park/neutral?

My last edit crossed with Marty's post.. which seems to rule out the vac line scenario.
I've posted my suspicions etc about a TV fan on a P38 I converted recently and talked in general terms about things like LPG reducer and alternator noise, to prevent confusion and aid readability it's time for me to step aside and let P38 experts talk now :-)

Doesn't sound anything like a road/jet engine sound so I think I can rule out the viscous fan.

I've been out at lunch to fill up the LPG tank and it's still not doing.

As for the year, it's a 51-plate/2002.

I'll have to wait for it to come back to test it if it happens on both fuels but I know if happens when in park to - I had a play about with it when stopped at some traffic lights the other day.

The car that used to belong to OldShep that was bought by one of my neighbours had what he'd been told was a whistling alternator bearing. I took the belt off and it spun freely with no sign of any noise or roughness. Put the belt back on and used a long screwdriver as a stethoscope and found it was one of the idler pulley bearings. It had got to the stage that you could hear the noise from that over the engine noise but spinning it with the belt off and it felt fine.

Wouldn't want anyone else who's car I've converted to think there's a problem with their fan. Tried to be helpful with the fan thing, I know I did notice a noise on a P38, had it in my head that it was a fan, maybe I remember wrong and thought it was the idler pulley at the time. Checked to see if I made any notes on this (I sometimes make notes on cars I convert, either tech aspects of how I fitted/setup the LPG install that might speed up conversion of the same model next time or if I find an issue with the car itself) but didn't make any notes. Sometimes I'll put a 'further advice' section on the receipt (only if I think the customer would want me to do that, some wouldn't for obvious reasons) but I didn't put an advice section on the receipt either.. So can only go on memory which seems to have failed me this time!

I think my "Further Advice" was to investigate the misfire codes, bad MAF readings and check the O2 sensors.
After changing both lambdas and the MAF it's running like a top!

That's good to know Miles, I'd forgotten I'd done you a further advice bit.

I managed to get it on video yesterday!

Happens on both fuels, with the air vents on and off and it happens when parked as well as when driving.

I'll upload the video tonight.

Video: https://youtu.be/AH762j6Cm9M

You haven't got the stereo on have you? That sounds like alternator whine through a stereo usually caused when the bonnet earth strap isn't connected or an alternator suppressor isn't fitted (but there isn't one on a P38 anyway). Does it get louder if you turn the stereo up?

You sure someone hasn’t swapped out your lump for a tdi, sounds like a turbo whistle, definitely one to think about,,

Not making that V8 rumble they haven't. What exhaust are you running David? It sounds wonderful.