Intermittent Squeak at rear of 2010 Lexus 450h

[Kelvin Lax]

I've recently purchased a 2010 Lexus 450h 85k miles. It has developed an intermittent squeak when on the move. It is very irritating. It's been to the garage who changed the tailgate bushes, having initially tried just greasing them. It's better but there is still a noise. Has anyone else had this problem? Is it a known fault? Don't think I will keep the car if it can't be remedied as can't stand it. This is my 2nd Lexus and love the car otherwise. Ideas please.