UK-POLOS.NET - THE VW Polo Forum

Thanks for the link. My feeling is that the noise comes initially from the tyres and passes through into the cabin without exciting any particular panel modes. The reason I say this is because the frequency doesn't change with speed. It just gets louder from 20mph until about 60mph when other noises, such as wind, become dominant.
When I got my first new car - a Mk1 1600 Golf GTI - I put BBS alloys with Pirelli P6s on it. They initially made a similar noise but this disappeared after they were run in - about 1,000-1,500 miles or so. I get the impression that the noise comes from the blocks of tread vibrating on the tyre carcass.

In you thinking about the causes of the noise, have you considered box-section and panel resonances? These are not just general structural vibrations but instead are peaks in vibration brought about by the shape, position and material type from which a part's made. I don't doubt that VW's designers use computer modelling to predict such resonances. Sometimes the placing of a quite small dampening mat or fibre bung on an area that's predicted to otherwise vibrate and end up resonating can curtail it enough. There's visible evidence here and there on my 1.2 that VW goes to some extraordinary lengths to tune out the worst of these. I imagine they treat the more expensive Polo editions more fully than the cheaper ones, though.

On my old Golf GL, which had quite minimal onboard sound-proofing, (and not withstanding what I've said about the effect of the suspension) I made a definite worthwhile improvement in the level of noise intrusion by fitting the following:-

1/2-inch thick, medium-density fibre matting triangles, to the underside of the bonnet, underneath the Golf's official acoustic bonnet blanket;
Pliable black mats fitted down on to the floorpan, underneath the foot positions of the carpets;
Pliable black mats fitted underneath the rear seats;
Additional pliable mats added to the interiors of the doors;
1/8-inch thick, high-density fibre matting added to the underside of about half the roof (the roof came with a sunroof, so this required some special care);
1/2-inch thick, medium-density fibre matting laid in the bottom of the spare-wheel well (avoid lining the sides of the wheel-well, as this can often then prevent you from getting the spare wheel, particularly if it's a full-sized one, back into the well);
Pliable black mats added to the rear suspension haunches in the boot.

I used a kit supplied by BJ Acoustics (Oldham), sadly no longer trading. Still got the receipt and the pre-purchase samples.

I think you'll agree that, for me, that involved an awful lot of physical work, some of it pretty back-breaking. Most DIYers wouldn't have done it themselves.

I also changed the Golf's tyres for Michelins. The Golf originally came with Continentals (on steel wheels) but I then proposed changing them for hopefully quieter Michelins, and so I roped Michelin themselves in on the problem. Michelin sent out their tech manager to visit me (this was about 25 years ago, when some companies actually practised what they preached when it came to customer care) and we drove around my locality discussing the issue and which Michelins would likely make a noticeable difference. I'm pleased to say that, from both my point of view and Michelin's, the most cost-effective choice was subsequently made.

veteran wrote: Sat Apr 28, 2018 4:20 pm Some of you might be interested in a UK firm that makes noise-suppression kits for a number of vehicles, and I think that includes the Polo. Go to http://www.nkgroup.co.uk. I think that, some years ago, NK bought out BJ Acoustics, an Oldham-based firm that specialised in providing to DIYers all sorts of anti-noise kits for cars. NK's prices are quite steep, though.

I have now got that kit (£221) and I intend to fit parts at a time, to see which has the greatest effect. I have just fitted the 2.5mm spare wheel well adhesive pad, the 10mm boot mat and the 10mm mat under the rear seats. I would have fitted the adhesive wheel arch pads, but I could not see how to get the boot linings out.
The noise appears to have got worse! This makes no sense, so I think what has happened is that some other noises have been reduced and the problem noise has become more easily identifiable. I cannot believe it is tyre noise, or even suspension noise. It is detectable at about 10mph now. If it were bearing noise, it would probably be louder if I opened my windows. But opening the windows makes no difference apart from adding wind noise.
I am somewhat flummoxed!

Crikey, that was quick of you. For myself, I've been intending in the longer term to contact that firm to get more details about their various kits, but it's low priority at present. I suspect, however, that because on the production line VW fits to Polos, as standard, bituminous pads on the floorpan under the carpets, the interiors of the doors, and a mild amount on the roof, the only parts I'd need for my own Polo would be some pads to fit to the underside of the bonnet, a thick mat to go under the back seats, and a roundel of thick mat to lay in the bottom of the spare-wheel-well.

But treatments come with their risks. It might be that, due to differences in tyres and some chassis parts, the acoustic tuning of your GT has now been thrown out of balance, or it could be that whilst some of the high frequency noise has now been suppressed by what you've done, it's unmasked the lower frequency noise and that LF noise is therefore now more noticeable.

Let's face it, noise inside a car can only come from two or three specific sound energy sources: (i) wind noise (ii) vibrational/combustion noise from wheel bearings/engine/gearbox, and (iii) tyre frictional noise transmitted upward through the suspension. I know you've strong reasons for believing otherwise, but my guess is that what you're now hearing is largely LF noise and boom, coming up from the tyres/suspension. If the GT has tighter suspension - which I suspect is the case - then more roadnoise will be transmitted up via that path anyway. Also, if you've got wide tyres, those too will increase the noise. The purpose of add-on pads and mats is to attenuate and deaden the noise energy once it gets into the chassis/shell of the car, but doing this with any great effectiveness can only be done by a suck-it-and-listen approach (unless you've enormous technical resources to hand for predicting the result), and in my view it's best done piece-meal, a bit at a time, so that you can see which parts (and where) are most effective.

One thing that might be worth you checking is whether, underneath the car, all floorpan holes, cill holes, and box-sections are properly stoppered (post wax treatment). If not, one or more could be resonating at some low frequency, at certain speeds. It strikes me also that the large plastic undertrays now used on 6R/6C Polos could drum if not screwed down properly.