30mph vibration

Hi need a bit of help here,

Went off roading weekend had great time but when i left my 300 disco developed a vibration through the steering at around 30mph. Its worse in second at about 30 but not as bad in third, but when i dip the clutch magically it disappears...

Any ideas on things to look for or has anyone experienced this, gonna start with taking front prop off and see any improvement...

Would the wheels maybe need re balancing thought taht would affect more 60-70mph...

Any ideas would be great...

dipping the clutch dont stop the front prop rotating!

Check for big clumps of mud inside yer wheels and inspect the steering damper, take the damper off and give it a drive even.

I thought by taking the prop off might help deter weather its transmission to front axle or not all be it i would have thought it would do it more than just at 30mph...

Took car and pressure washed the wheels brakes and hubs, will take wheel off next and have a proper look...