Rena XP2 resonating

[jksgoh]

hi,
just got a rena xp2 to replace my old fluval 304 which died of old age.
anyway setup was nice and easy and got a good flow coming out.
the filter itself (ie the big box which filters it all) is quiet and i have no complaints there. However, the outlet (the spray bar) resonates with an extremely high pitched noise. the noise disappears when i turn the little valve to slow down the flow of water, but only when its almost completely shut, or strangely when the spray bar is facing downwards... i have mine facing angled up to agitate the surface of the water for o2 reasons.
.... now without having to replace the spray bar with an aftermarket one, does anyone know of how to fix this????????????????????
i must say..... it really gets on your nerve (the high pitched noise that is)!