Rattle at low rpm under load appeared overnight - 6C 1.0

[dubu]

Hi all, sorry that my first post is asking for help but here we are

I woke up today any my polo is making a rattling noise, it seems to be mostly at low rpm (lugging range) with some load but irregularly at slightly higher rpm too.

It's very apparent going up slight hills at ~1800rpm, and on the flat accelerating between 1200-2000. Above 2000 it doesnt really happen. It also only seems to happen in 3rd and up, not 1st or 2nd, although it doesnt lug even accelerating up hills at low rpm in those gears anyway.

I spent a while trawling google and forums for similar things and tried all the things suggested, I shook everything in the engine compartment, the exhaust heat shield seems to be decently attached, it has a bit of flex but that seems normal? I didn't lift it and check it from below, I just poked the bit thats visible inside the engine bay.

I of course took everything out of the glove compartment and centre/door pockets (good excuse for a clean I suppose), it seems like its coming from the engine bay or under the car.

I don't notice any difference in the engine feel or efficiency, but I didn't drive it a ton. The sound also isn't really audible with the window down/driving by a wall, it just sounds like the car is lugging a bit. This makes me think its resonance from the engine lugging causing a loose part to rattle, but I can't find what it could be. I thought about getting a bottle of fuel system cleaner or something to perhaps see if its actually engine related but not sure if thats a good idea.

Here's a sound sample (from 0:08)
Sorry I cut it early, but it goes away when you hit 2000 rpm.

Anything I could try to diagnose it?

[RUM4MO]

If it was coming from the engine and only under these operating conditions, then I'd suggest a slight bit of pinking/pinging, you could load up with UL+ to see if that clears it.

The other thing, again if it is engine internal/combustion rattles, is that all these modern engines have extremely low friction piston rings and that can allow engine oil to get into the combustion chamber and as that lowers the effective octane rating of the "fuel in the cylinder" that can cause a similar situation to the old pinking/pinging, but now gets called LSPI, some engine oil manufacturers have addressed that by improving their "brews", I will only ever use Mobil One ESP to API SP or above in my VAG cars, I don't think that any of our cars have suffered from this, but it can be a killer, so I'm just playing safe and taking precautions to avoid that being an issue.

As you say, a forced resonance from within the engine compartment could also be the source, but initially increasing the octane rating of the fuel you use, or just using a "proper" fuel brand (who knows nowadays what that means!), could sort this out - or allow you to consider other possible sources.

Edit:- my wife's old 2002 VW Polo 1.4 16V used to pink/ping under these conditions, and I changed it to UL+ and that sorted it out and made it a lot more drivable at low revs - entirely different engine to your one though! I eventually worked out that it was the oil/air separator that was not stripping out enough of the oil out of the crankcase fumes, and that meant that it was burning - and so using - engine oil. I did replace the oil separator with a genuine one, and that reduced the engine oil usage - my wife did not allow me to revert back to it using ordinary UL petrol though as she had got used to the improved drivability!! Your car's engine also has an oil separator and some people seem to have found the need to replace them at higher mileages.
What is the current mileage of your car, what brand of engine oil and what grade/weight is the engine oil, and finally what brand of petrol are you using?

[dubu]

It did cross my mind that it sounded a bit like pinging, the engine is at 53k so relatively low for that I'd have thought? I'll try topping up with 99 and seeing if it makes a difference. I usually top up regular at the local Esso garage, I'd guess that counts as "proper" but like you say, who knows these days.

I actually forgot about this, but a couple of months ago I had it in for an MOT and they decided to change the relatively fresh oil. I didnt think much of it at the time but I didnt actually ask what weight they used. Usually I use 5W30 and I have to admit usually I just buy a brand I recognise lol but I've never had an issue. So right now, its mystery oil, but it seems to have been fine for the past couple of months.

I tried poking around underneath to see if I could find anything loose but no luck, I think I'll get one of the local garages to lift it and have a look. It feels like one of those things that will either be immediately obvious or a total mystery.

[RUM4MO]

Yup, I'd agree that Esso is a "proper" petrol brand, and actually my preferred one - although, my wife having a Costco account, does mean that while filling up locally it will normally be Costco, when away from home, I always aim to use Esso.

Maybe a full tank full of Tesco's finest, as it sounds like it is the highest octane petrol, would suit you better for this "trial" as Esso UL+ is quite expensive for this trial.

[dubu]

Well, took it into a local place I'm friendly with to have it sanity checked on the lift to make sure it wasn't anything obvious like a heat shield or suspension part and no luck.

I also ran 30 miles on Esso Supreme+ 99, I filled it up from 10% so I'd definitely expect it to have made at least some difference if it was related but no, so I guess that narrows it down to a mechanical rattle. Not sure if that helps my sanity or not lol.

I guess the next step is just to book it into a VW specialist, not sure I'd trust one of the local rural places to find something potentially obscure in a reasonable amount of time and I'd rather not pay for them to scratch their heads, or waste their time.

[RUM4MO]

Oh well, you've tried the easy way to be able to hopefully discount that it is just internal combustion noises, where are you located roughly, there are quite a lot of VAG Indie workshops around in Scotland?

My local rural workshop seems to be a VAG type of person, well the owner anyway, but maybe not up to date with these EA211 engines - yet.

Edit:- just another thought, is this a TSI engine? It might just be the turbo actuator rod issue.

[dubu]

Not a turbo, just a piddly little NA 1.0. It feels quick enough as long as I don't need to accelerate above 45 and can't complain about 60MPG.

I'm on the west coast out beyond Dumbarton, had good experiences with JR VW centre in Paisley so I'll probably see if they can have a look.

[Tracendaz]

I've had a similar experience in my 2015 6c 1.2TSI, a strong vibration/buzz/rattle under load. I initially thought it was under the driver's footwell and found some Golf and up! owners had rattling fuel lines where the clips had failed.

The local garage couldn't find anything amiss, and it needed sone aircon work (local garage don't do that), so I took it to the VW specialist in Petersfield who found that the backing plate for the front offside brake disc was worn and rattling. They changed it and the rattle has gone! Might be worth checking the brake disc backing plates.

Good luck! Tracendaz.