Knocking noise at speed

Hello.
I did do a search and did not seem to find a similar issue.

I've got an 96 Isuzu Mu (Rodeo) with Manual Hubs.

Recently I have become aware of a knocking noise from the wheels which only appears at speeds greater than 30mph. The sound and reptition of this noise is like there is a stone lodged in the tread of the tyre. But the noise does not happen at lower speeds.

Any ideas would be greatly appreciated.

Thanks

Ha Found the source of the noise!

The big lead balancing weight for the front tyre has just fallen off.
So I guess that at speeds wind resistance caused it to rattle.