Hi, I am hoping someone might be able to help......
I’ve noticed a pulsating thrumming or droning noise at slow speeds. It’s loudest at 30mph but still evident underneath road/engine noise at 45mph.

It’s independent of engine revs (coasting and revving doesn’t change it). It’s independent of gear selection (manually holding in gears makes no difference) Its independent of engine temperature.
It’s clearly something in the drive transmission somewhere.

The dealer has checked all the obvious things and said it was a wheel bearing. They changed it....it’s still pulsating just the same. They now confess to be “scratching their heads” and want it in for an extended investigation.

Because it’s a rhythmic noise as opposed to a constant tone I didn’t think it was a bearing sound ...it’s more like the sort of droning/throbbing noise I got heard from the differential on my old banger when I was a lad ( a million years ago)
Obviously they are the trained technicians on modern cars but I wondered if anyone out there has a suggestion I could feed into them while they are scratching their heads? I don’t want my car to be sat in their workshops any longer than necessary.
Thanks

Could be tyre noise. Did the noise start suddenly?

Sounds like tyre noise, what we in the industry call ‘heel & toe’ wear. It can occur on any tyre, and is generally influenced by tyre pressures and vehicle settings. To identify it, look at the tyre sideways on. It’s also known as saw tooth wear due to the way the trailing edge of the tread blocks wear quicker than the leading edge. If you run your hand circumferentially from the rear of the vehicle toward the front, there’ll be little or no resistance from the tread blocks. Run it from front toward rear, it’ll feel like ridges, and the tread blocks will be sloped front to rear.
Most tyre shops will tell you it’s a faulty tyre and try to sell you a new set of tyres, what you can do, is rotate the tyres n the vehicle, I tend to advise diagonally from front to rear. It won’t cure the noise immediately, and may take a few hundred miles, but if you can live with it, it will improve and save you a few quid.

And just in case your technicians try to fob that off, I’m a tyre engineer, and worked for tyre manufacturers for almost 23 years, working for Bridgestone, Continental and Hankook.

Interesting. Thanks for the replies.
The frequency of the pulse doesn’t seem to change speed much whether at 30 or 40mph. Would not a tyre issue change frequency with that sort of rotation change? I’m thinking of occasions when I’ve experienced a balloon over the years....it seems to respond to road speed and change sound pulse. This doesn’t.

The noise ‘developed’ quite suddenly ...perhaps over two or three short trips to the supermarket getting louder before we noticed it. The car has obviously been sat a lot this last year...outdoors. It’s my ‘feel’ that when I first set off (first 1/2 mile) the noise isn’t as loud.

To test the tyre suggestion could I affect a change by (significantly) changing pressures for a short test drive? The tread depth is pretty even at 5mm across the rears ...the fronts are both 4mm at edges and 5mm in centre (the dealership did a videoed ‘safety check’ around the car while it was on the ramp)
Could I just swop front pair to rear and see if the noise changes in any way immediately?