Another funny sound

[Joeauger]

When driving the car it makes a repetitive thud.
The faster you go the faster the noise gets but not really much louder.
I’ve had a quick look under the car but can’t see anything dangling out.
I really don’t know where to start to look for a problem so if any of you have any ideas…
Thanks

[Bigfeet]

A thud noise?

Sounds daft but did you check the tyres to make sure that there wasn't a stone or a nail caught up in them?

[Joeauger]

There is a stone in one of the tyres but that is making a different noise. This noise sounds like its coming from the middle of the car.

The noise sounds similar to when you drive over the lane markings on the road.

[lfcrule1972]

Is the plastic sump guard loose ? Has it lost some clips so that it's buffeting in the wind as you drive ?

[Toxic]

Tyre pressures ok? if its a rumbling sound could be a wheel bearing i guess, what miles is on the car?