I've been having a problem with the tuning pegs on my bass recently. They rattle sometimes when I'm playing open notes, has anyone any ideas on how to remedy this?

I've tried tightening the screws on the pegs but they still seem to rattle.
My Gear:

Peavey Grind NTB 6 (6 string)
Cort Action Bass (4 string)
Roland Cube 30 amp
Boss ODB3 Overdrive

Ibanez JS100
Peavey Vyper amp
Korg Toneworks AX3000G multieffects
Dunlop Cry Baby 535Q Wah
Big Muff