64 transit custom LWB sounds like a tractor at 2000 rpm?!

[Michaelnot]

Hi got a 64 transit, started to notice a loud noise inside the cabin when accelerating. Comes on around 2000 rpm and fades after 2000? Took it for a service and mentioned to my mechanic but he didn’t see any cause for concern. But wanted to check if anyone else has had a similar experience and how they may have resolved?

I’ve driven many transits and never noticed this before.

Any help would be greatly appreciated.