Whining from rear

No it's not the kids ! My car has recently developed a whining noise from the rear - it is more noticeable when decelerating rather than accelerating and is particularly obvious when travelling at 30 - 35 mph. It doesn't sound like engine - more like transmission or other moving parts. There is no loss of power and in all other respects the car seems to behave normally. Have any of you experts out there got any ideas of possible causes ? I have just had all 4 wheels refurbished but I cannot imagine that the sound is anything to do with wheel balancing. The car has only done 28000 miles and is regularly serviced. Thanks for any help. Chris

Is it engine speed related or ground speed relayed ? If its engine it could be air con compressor /water pump/assoc pulley bearings If its ground speed then maybe a wheel bearing/driveshaft uj Good luck !

Thanks for the comments - it seems to be ground speed related - it disappears when accelerating hard. Your comment about air con compressor is interesting - I have recently had the air con lateral pipes replaced. Any further thoughts from all you experts would be welcomed before I ring my Indy to get an opinion - I need to know whether it is a 3 figure cost or (God forbid) a 4 figure cost ! Chris

Have you checked the SAI? http://rennlist.com/forums/996-forum/735878-sai-repair-diy.html

The SAI pump shuts down 30 seconds after starting, so I doubt it is that. If it is related to ground speed, and only when you decelerate (presumably with a gear engaged) then it sounds more like transmission to me. Possibly diff bearings. Or is it a different pitch depending on which gear you are in, or maybe only in one gear? That might indicate a gearbox bearing, but I'm guessing, and hoping I'm not putting the wind up you. Best get an experienced ear to have a listen.

Thanks Richard. Whatever it is, I think it is in the early stages. As you say, best to get an 'experienced ear' to listen to it. My apprehension did however take the shine off a beautiful 100 mile drive through the Northumberland countryside last Saturday ! - hopefully the car will soon be sounding sweet again. Chris

Yes that's right under normal conditions, but they can run at anytime according to "Loren" over at Rentech (who is as you know a knowledge base and Admin) and one of the things that will make them run is moisture or valve faults I think. And they will run when when slowing to a stop apparently. But probably all visible possibly on Durametric? Richard?

From your description Chris, I'd agree with Richard's comment that it's probably transmission-related, particularly since it's more noticeable on the over-run rather than under power. As far as the diagnosis is concerned you could check to see if you get the whine in top gear, one of the intermediate gears and also in neutral (I'm assuming you have a manual 'box). If all three then it's most probably associated with the final drive but, regardless, would require a full transmission strip anyway. Having said that, I do hope that it turns out to be something simpler and cheaper to fix. Jeff

I just checked, and it only runs for 50-179 seconds, depending on the conditions at startup. It is switched by a relay controlled by the DME, so unless the DME or relay are faulty, it wouldn't run if a valve had stuck. You can activate the SAI pump with a PST2 or PIWIS, but I'm not sure about Durametric (I would expect you can though).

Snap!! mine is doing the same mostly in 3rd and 2nd under 2000RPM decelaration Been reading a few views on this and pinion bearing is coming up. I am from north east England be interested to listen to both cars see if the cars share the same sound Regards Simon

Just out of interest, does it make the noise if the air-con is switched off ? Mine made similar noises, but most noticeable just above idle, related the aircon pressure being low. Noise could not be detected on acceleration because of induction/ exhaust noise, possibly explaining why if it was aircon you only notice it on the over-run. Noise obviously dis-appeared if aircon switched off, to return as soon as aircon switched back on. My noise dis-appeared as soon as the aircon was re-gassed. Paul 2004 996 C2 40th Anniversary

No it makes no difference in mine if Aircon is on or off, whines from 2200 rpm on decelaration and gets louder the lower down the revs. No noise on acceleration.

Just an update for those interested. I decided to leave things until my next due service in February, since I do not use the car during the winter months, and I hoped to get everything sorted at the same time. On starting the car yesterday for its weekly warm up, I got a red warning light for low coolant level. I topped up the coolant and it took about half a gallon ( including suitable antifreeze ! ). I then took the car for a short run to bring it up to running temperature, and there was no strange noises ! Could this have anything to do with the 'whining' or am I just clutching at straws ? Chris

Water pump! That was a fair amount of coolant missing....

Hi, Check the belt pulleys. I had a similar untraceable noise last year on my 996 C2. Eventually found out what it was when the lower belt jockey wheel sheared. Not an unknown problem as that area of the engine gets a lot of road muck and wet and the pulley wheel shaft corrodes with time. Worth a check.

A final update on this one for anyone who is interested. Took the car in to my Indy for its annual service and MOT last week - told him of the strange sounds and coolant loss (although since filling the coolant I have not had a re-occurrence of the 'whining'). He had the car for 3 days and did all appropriate checks but couldn't trace any faults - still a bit of a mystery, but the majority view of the lads in the workshop was that there had been an airlock in the coolant system and the lack of coolant had caused the 'whining' from the pump. Anyway, all seems well now, and the car is ready for its 2 tours of the Borders coming up in the next 3 months - I am determined to put more miles on the clock this year than the 1100 I did last year ! Chris

1100 miles is really not good for a car and I don't actually believe its a good thing to have a weekly warm up My dad used to do this and wondered why his battery kept going flat Mind you it was a Maestro !!!!!!!!!!!!!!!!!!!!!!!!

I had a Maestro once - worst car I have ever owned - front wheel bearings fell apart in 18 months from new !

Lol, I was unfortunate enough to have one as well. I think it broke down at least every week. I had the Mg badged 2ltr. Went like stink though in between being broken.