R230 SL350 Droning/humming noise?

[derin100]

So, I've recently purchased a low mileage (30K miles) 2008 R230 SL350.

I've only driven it about 300 miles myself so far on two long day out trips so I'm still very getting used to it. Everything seems really nice and drives really well. Except on today's trip of 175 miles on mostly A-roads and Motorways of varying speeds, I had the chance to 'listen to it' a bit more and I've noticed that under certain conditions it not as quiet and refined as I'd imagined it would be.

There appears to be (and I don't think it's my imagination) a kind of low level droning/humming noise. This seems to only be at quite moderate speeds of say 30-40 mph. And, I think more noticeable on over-run (i.e. off the accelerator). For example when slowing down coming towards a roundabout. And that's quite an annoying speed for it to happen because one is often stuck at around that speed.

Initially, I was thinking maybe it's road-noise off the tyres. But, they are the Dunlops specified by Mercedes (MO) and not run-flats. On original option 18" MB wheels btw. And on its standard original SL350 suspension with no modifications. And there's no significant vibration that I can feel. Just this drone/hum!

It's difficult to even point where exactly it's coming from but I don't think it's from the very back. It sounds or 'feel' more front or even right in the centre in the region of the transmission tunnel.

I'm thinking along the lines of a wheel-bearing? Or a propshaft bearing? But after only 30K miles on an MB SL?

Any other thoughts or suggestions?

It doesn't appear to affect the way the car drives at all but if there is 'something amiss' I'd rather get it sorted sooner rather than later as at the moment I still have 2 months of the 3 months warranty I was given by the dealer yet to run.

It's my first R230 so maybe they're just like this and make more noise than I thought they would but I've had 64 cars in my time so far, including earlier variants of SLs, and somehow this droning doesn't seem right.

Many thanks in advance

 

[TheBlimp]

Hi.

I have a similar noise coming from my MB CLS.

Mine is more than likely the tensioner pulleys on the front of the engine or possibly serpentine belt or a combination.

Might be worth having that looked at?

Cheers

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[flowrider]

What Dunlop tyres do you have, how worn are they? Being MO spec doesn't actually mean much.

 

[Monkeylegend]

Had the same issue on mine with 48k miles on it when I bought it, same as yours, 350 on standard suspension. Didn't really notice it on the test drive and it was worse on smoother roads at 40/50 mph.
The front tyres were about 7 years old and the tracking was out slightly. Replaced the front tyres and had the tracking done and all was quiet. When I ran my hand back over the edge of the tyres you could feel the ribbing where the outer tread had worn.

 

[derin100]

Hi.

I have a similar noise coming from my MB CLS.

Mine is more than likely the tensioner pulleys on the front of the engine or possibly serpentine belt or a combination.

Might be worth having that looked at?

Cheers

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Yes, it did cross my mind that it could be pulley tensioners...it certainly has that sort of sound to it. Do you know how one can test or check that whilst the car is static?

Thanks

 

[TheBlimp]

Yes, it did cross my mind that it could be pulley tensioners...it certainly has that sort of sound to it. Do you know how one can test or check that whilst the car is static?

Thanks

Hi,

The garage I took mine to used a stethoscope to listen to the pulleys individually.

If you can loosen the belt you should be able to spin the pulleys freely, any that stick or are noisy may well be the culprits.

I found this YouTube video that somewhat explains.

Thanks

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[derin100]

What Dunlop tyres do you have, how worn are they? Being MO spec doesn't actually mean much.

The tyres are as follows:

Front: Dunlop SP Sport Maxx GT MO 255/40/18 DOT 0214 Tread a good 5mm

Rears: As above 285/35/18 DOT 1015 Tread a little less say 4mm ?

So not 'new' tyres but by the DOT not excessively old either.

 

[derin100]

Hi,

The garage I took mine to used a stethoscope to listen to the pulleys individually.

If you can loosen the belt you should be able to spin the pulleys freely, any that stick or are noisy may well be the culprits.

I found this YouTube video that somewhat explains.

Thanks

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Ah! Good! (recently retired surgeon here...so I have plenty of spare stethoscopes lying around the house!). I've done a fair bit of home mechanics in my time but never loosened or tightened a multi-belt myself. Is it easy enough to do?





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[derin100]

Had the same issue on mine with 48k miles on it when I bought it, same as yours, 350 on standard suspension. Didn't really notice it on the test drive and it was worse on smoother roads at 40/50 mph.
The front tyres were about 7 years old and the tracking was out slightly. Replaced the front tyres and had the tracking done and all was quiet. When I ran my hand back over the edge of the tyres you could feel the ribbing where the outer tread had worn.

Very possible in my case too then. As my tyres probably aren't going to last too much longer maybe when I put new ones on that will cure it and in the mean time I could just live with the drone until they're worn out.

It's difficult to find smooth bits of road to test the theory out, huh?!

 

[TheBlimp]

It seems fairly easy.

If you Google it there are plenty of videos showing how it's done.

Just be careful of you're going to remove the belt completely as people forget how they go back on. Worth taking a picture as they tend to snake all over the place.

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[derin100]

It's certainly reassuring to know that I'm not 'just imaging it' though. I had my wife next to me as a second opinion...and her opinion was of course:

"What noise?"

Very helpful!

 

[derin100]

Thanks. Yes! That would be just the kind of thing I would do i.e. forget what pattern it went on.

 

[TheBlimp]

Thanks. Yes! That would be just the kind of thing I would do i.e. forget what pattern it went on.

Yes exactly. Me too [emoji16][emoji15]


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[derin100]

Just to feed back on this now...

I've now had the car checked out by an MB specialist. I wanted to do this before the 3 month warranty expired from the dealer that I bought it from 'just in case'.
Anyway, it runs out it's the tyres! Although they have decent tread and aren't that old they are deformed probably through lack of use.

So, as I'm faced with the prospect of replacing all four tyres I'm wondering what I should go for? Should I go for the same again? Where's a good place to buy from etc. for what is not going to be an insubstantial buy!

As mentioned above, what's currently on the car is as follows:
Dunlop SP Sport Maxx GT (MO) Front: 255/40/18 Rear: 285/35/18

Thanks in advance.