Rumbling noise (intermittent)

[DijonR]

Hi All.
On a recent trip from Swakopmund to Cape Town my 2002 3.2 DiD started to make a loud rumbling noise. Since I was alone in the vehicle it was difficult to tell where it came from, but my first guess is that it was a front wheel bearing playing up. I have had several of them over the years, in various vehicles, so that noise is quite familiar. At times it was so bad that I feared a bearing failure was imminent. The only peculiar thing about it was that the pitch fluctuated. It would remain at a high frequency for a while, then rapidly drop to a very low frequency, and then return to a high frequency again. If I were to explain that sound to a frequent flyer; you get exactly the same effect on these regional turboprop aircraft when they cycle the props prior to takeoff, or when they shut down the engines.
That noise remained with my all the way to East London, and then promptly disappeared! Because of Covid19 I have not done any long trips since, but I am just worried about something lurking in the background, waiting to strike again.
Any ideas?
Regards,
Deon