Hampton Roads Club Mini

I've had my 2006 Mini since Feb. 2011 and thankfully, we havn't had much heavy rains where I'm driving.  I was wondering if anyone else experiences a significant vibrartion when at highway speeds (50-60 mph) during Heavy Rain events?  It is comparable to running over rumble strips right before a stop sign or signal.

Funny thing is that when I take it out of gear and coast the vibration is gone.  When I downshift into 4th and run the vibration goes away for a while but will start up after about 5 minutes.  I then take it out of gear again and coast and put it into 5th and the vibration is gone. 

Basically about every 5 minutes I will have to either shift up or down between those two gears to maintain about a 50-60mph speed.

This ONLY HAPPENS when it rains HEAVILY.  When the road is wet with a light shower, I don't notice anything.

Ideas?  I used the search function above and searched for vibration. Sorry if it's a repeat.  It's my first Topic - be patient with me.

 

That sounds damned odd.  Makes me wonder if it's the traction control going berserk or maybe the ABS doing funny stuff because the heavy rain is making the car think that it's sliding rather than driving due to rotational speed differences between tires in a heavy rain.  Please post the cause of this when you find it, my curiosity is piqued now...