Vibration from the rear

[bigdods]

Recently had the suspension laser aligned and one of the suspension adjusters replaced as it was frozen. Handling was lovely until today..took her out for a hoon and above 70 a nasty vibration sets in from the rear, getting worse as the speed increases. Could this just be a wheel out of balance or is it something more serious ? Got her booked into the local garage on Friday to have the rears off for a rebalance plus they are going to check that everything is where it should be nothings come loose etc... any help on possible causes would be good

cheers

Dodsy