Hi Barry,
At the base of the assembly where it joins the ballast there is an area which is round and probably covered with
a black silicone type material. It is probably domed , indicating that the mounting bolt below it is loose. Remove the
black stuff and see if tightening the bolt does the trick. There is also a (i think) a rubber sleeve around the bolt. If tightening the bolt is not possible then replace the sleeve. Then fill with a polysulfide or silicone.
Fair Winds,
Eric