unwanted SK1 line out noise

[boneless]

hello all.

at the moment I'm working on an SK1 - just fitted highly liquids MIDI retrofit (http://highlyliquid.com/) which works great - and starting to put some bends in.

I've removed the speaker and put in a line out.

1k resistor to ground, 10k with 10uf cap to line out.

My only problem is a constant high pitched noise in when plugged to speaker (it sounds like some kind of oscillation)

Anyone any ideas why this is happening?

(it's darn annoying!)