whailing/whistling sound

I have a chevy kalos 1.2. For about 2 months its been making a whaling sound .the sound stops when i accelerate.at first i thought it was one of the belts. I had a new timing bełt and water pump put in and the vbelts changed.still the same. I noticed that when i take the oil dipstick out when engine is running the sound stops.somewhere on google i found a thread that i need to change an oil seperator valve membrane.any tips?

Maybe a case of low transmission/steering fluid or the belt is not tight enough.

Problem solved..crankcase breather valve needed to be changed