faint rumble while turning

[rh71]

'10 MB C300 with only about 14k miles - during slow turns such as on local roads or in/out of the driveway, regardless of forward or reverse, we're feeling a faint rumble when we turn the wheel before it even reaches full radius. Both directions left and right, both directions driving forward and backward, and ONLY WHILE IN MOTION. Leaving the car stopped with the wheel turned does not produce the problem. There is no vibration in the steering wheel at any point.

It is barely audible and more a feeling in the seats - like if you were to drive on those highway anti-sleep bumps, but not anywhere close to that severity. I want to say it feels like something in the rear but not sure how that would be possible. Visually nothing weird is happening at the belts. Any ideas?

As a history, we did have the original alternator replaced last year after it started making squealing noises. Apparently there's some noise at start-up now too but goes away quick, though I didn't hear it this time. Could this all be some drive-belt related?

 

[phucheneh]

Some stuff on this forum, I can really easily lead people through a diagnosis. Or sometimes, there's just an immediate 'oh yeah, that complaint. That's an easy one.'

This...I think the best anyone can do is throw out random suggestions. Ultimately, without experiencing the problem in-person, I doubt we'll be able to really grasp what the problem is.

Based purely on your description, it sounds like it's just tire noise. Mostly going by the 'only happens while moving' and 'feels similar to bump strips on the side of the highway' bits.

FWIW, power steering issues typically decrease in severity when moving. The strain on the system is much less...think about how manual steering feels. The steering wheel is very hard to turn when you're sitting sill, especially on pavement. Put a slicker surface under the car, like a coated garage floor, and it becomes a bit easier. Start rolling, and it's a LOT easier. So I don't think it's related; but again, I'd have to actually hear/feel it to say whether or not I think it's typical P/S 'groan' or 'whine.'

What kind of tires are on the car? Size and brand/model, particularly. The shorter and stiffer the sidewall is, the quicker tires tend to develop wear patterns that will result in noise and felt vibration. Also, your sportier RWD cars tend to have much more aggressive alignment specs that make said irregular wear come about faster. I'd bet your car has something like 7-8* or more of caster on the front, at least a degree of negative camber, and a decent amount of toe-in. Rear is probably closer to -2* of camber, and probably still a little toe-in. Comparatively, an average FWD car will have maybe half the caster and camber and little to no toe on the front

Run your hand across the tread of your tires, particularly around the inner edges, and look for kind of a 'sawtooth' pattern.

How often do the tires get rotated? If it's never been done, I'd put money on it being tire-related. If done once...still quite possible. People, especially at tire stores, will try and tell you that you have an 'alignment problem,' but your car was essentially designed with alignment issues, per their definition. The overwhelming majority of cases of irregular wear will be fixed with more frequent rotation, and remain absolutely unchanged by simply getting an alignment.

 

[rh71]

^ I believe you're right about tires. Now that you mention it, we hadn't rotated tires at all. Due to low mileage, we've only done oil changes after 1 service A at the dealer 3 years ago. And I hadn't had to rotate tires on my vehicle (uni-directional & staggered) so it's been the furthest thing on my mind when it comes to taking care of this guy. Now I gotta find out if it's non uni-directional and hopefully it's not driven beyond "repair".

 

[phucheneh]

I would bet your car has 25-30k tires, at best...not knocking MB or the tire manufacturer...carmakers just tend to favor high grip and low noise over long life when it comes to what they put on brand new vehicles.

So even with frequent rotation for the rest of the life of the tire, they'll probably not have enough time to even out very much.

BMW is the only manufacturer where I've heard reports of directional tires on staggered setups. But IIRC even with cars that use asymmetrical staggered tires (marked 'inside' and 'outside,' rather than with a direction of rotation), they tell people not to rotate them...supposedly 'compromises' the handling of the car, as you would have to cross-rotate and the tires would no longer be 'broken in' to their respective positions on the car. Personally, I find that absurd. Not sure if they say the same about non-staggered tire setups that just be rotated front to back.