I have an annoying rattle started somewhere behind the dashboard/binnacle/steering wheel. It seems to depend on the road surface. It sounds like washers rattling on a loose screw. I have tried moving the steering column up and down, bumping it up and down, twiddling the knobs and switches, and still, it persists. I have no intention of dismantling anything to try to eliminate. I'll just have to live with it. I have had minor rattles before, particularly in cold weather, but they go as quickly as they come. This has been rattling for several weeks now. Perhaps if the weather warms up.
Maybe I should squirt expanding foam filler foam everywhere
I have had this exact issue, among many others, for 15 months now and it hasn't developed futher so fingers crossed yours will be okay. My issue hasn't gotten any louder since it developed and, as you say, is very much dependant on the road surface so it thankfully isn't there on the motorway where it would be at it's loudest.
As I said, It SHOULDN'T develop further, but that doesn't mean you shouldn't get it looked at if it's bothering you.