Hey everyone, my octy started doing this weird pulsating sound after doing a timing belt and water pump change and I first noticed the sound when it was doing a dpf regen. I asked the mechanic who did the change if he knows what's going on and he has no clue about that sound, but can definitely hear it. 

 

I'm wondering if any of you knows what this sound is. 

 

Thanks

 

Video of octy

Also the sound cannot be heard from the engine bay, tested it earlier with a friend and we could only hear it inside the car. For information it's a 2016 CRMB engine although the vin says its a 2017 model, is that normal? 

 

Try the test with the AC both on and off, (need to wait a while for it to change state) and report back if it stops or gets worse. I can barely hear it but if its what I can hear then it's what mine has developed.

Just tried with ac on and the noise goes away. I opened the expansion tank and after squeezing the hose, a couple of bubbles popped up. I turned the ac on again and set it to max temp and speed, see if it circulates the coolant. Later when I get home from work I'll open it up again and see if more bubbles pop out. 

But as soon as I squeezed them bubbles out after turning on the ac, the noise when the ac was on, was much quieter, almost impossible to hear but definitely no sound with ac on. 

On 05/10/2022 at 16:31, Apexy55 said:

Hey everyone, my octy started doing this weird pulsating sound after doing a timing belt and water pump change and I first noticed the sound when it was doing a dpf regen. I asked the mechanic who did the change if he knows what's going on and he has no clue about that sound, but can definitely hear it. 

 

I'm wondering if any of you knows what this sound is. 

 

Thanks

 

Video of octy

Did you solve this? I have the same sound but I haven't changed anything.

Did anyone hunt this one down? I have the exact same sound on my 2019 RS245. Getting the AC gas topped up in the morning to see if that is the culprit.

I've had a rhythmic noise similar to what's described here on my CXXB 1.6 TDI engine since owning the car.

No mechanic has had any idea what it may be. Timing belt / water pump change didn't change the noise at all (and nothing found on inspection of pulleys). In my case the AC doesn't affect the noise, however, I'm not sure what kind of compressor is in my car, so it may just be on at a low load (since we're not that warm a climate here in the UK!).

Soon as you put load on the engine (i.e. go to move), it stops. This is different to the rev up/down of the rpm assist feature where it'll rev up and if you don't pull off in so long it'll rev back down again, rinse and repeat.

I got the AC re-gassed yesterday. As part of this they renew the AC oil that's mixed in with the gas. AC specialist I went to mentioned that sometimes AC compressors can get noisy on old oil. At the moment, the sound hasn't returned.

The car had 65,000kms on it, and had lost only 10% of the AC gas since new. In any case the full 500g is in there now and it's happy days. If the sound returns I'll update here.

I should add that 11g of AC PAG Oil was taken out, and 39g put back in. Perhaps not enough oil from factory.

Extraction of the Pag oil amongst the refrigerant gas very hit or miss, the majority will remain in the pump and could only be removed by removing and upending the pump.

When I have evacuated systems there has been just a tiny mist and smear of PAG oil.

11g out is probably OK but they would have no way of knowing how much remains in the compressor they may have erred on the side of safety.

There are also set weights to be added for a regas, for a regas with new pump, for a regas with new condensor etc, maybe the chart shows 39g.

I have no means of measuring or weighing oil extracted, I never add oil with a regas unless its after repairing a leak which shows traces of oil, normal system losses are through the walls of the flexible hoses and its the gas that leaks and not oil (molecular size versus permeability).

Yes I've had the droning noise on a couple of vag cars whenever the refrigerant needs replacing, due to losses. I did wonder about the oil replacement most of the time mine did indeed show next to zero evacuated.

Update - pulsates for about 1-2 cycles, then stops, so still a win at the moment - used to go on for ~3-5 mins