I recently fitted 6 by 9's and had to chop through the centre metal rod going across my parcel shelf, this caused it to bang quite a bit, but i have now sorted it and thought id give away my secret for others haha 
what i did was got a few long strips of velcrow sticky stuff from halfords, stuck them on the plastic that holds the shelf up next to the speaker, then on the actual boot door itself i put a bit on there in the middle where the parcel shelf sits, this makes it more secure and also stops the banging
There is a peice of plastic that goes under the parcel shelf to hold it, put the velcro across it
Just under the back window is a part that the back of the parcel shelf rests on, this is where you put the velcro
I also took the two strings down and cable tied them to random bits in the back boot so keep that secure and down, now when i open the boot the parcel shelf doesnt come up but as long as it sorts the banging problem then it doesnt bother me as much
hope this helps everyone !!
what i did was got a few long strips of velcrow sticky stuff from halfords, stuck them on the plastic that holds the shelf up next to the speaker, then on the actual boot door itself i put a bit on there in the middle where the parcel shelf sits, this makes it more secure and also stops the banging
There is a peice of plastic that goes under the parcel shelf to hold it, put the velcro across it
Just under the back window is a part that the back of the parcel shelf rests on, this is where you put the velcro
I also took the two strings down and cable tied them to random bits in the back boot so keep that secure and down, now when i open the boot the parcel shelf doesnt come up but as long as it sorts the banging problem then it doesnt bother me as much
hope this helps everyone !!
