Whistling/whining From Wheels

[Luke]

We have an 05 plate citroen c3 1.4 diesel, early this year we had the front brake pads and discs changed as we could hear a high pitch whistling noise, the pads were indeed worn out and the discs were in need of a change. Anyway since then it occasionally happens and sometimes its louder than others(to the point it can be heard over the stereo), yet whenever we touch the brakes even just slightly it stops, then starts again as soon as you take your foot off. It doesnt happen all the time just now and again and it seems when were at high speed. I recently took the front wheels off with my father in law and noticed that the pads on the offside front disc were virtually stuck to the disc, after freeing it up we checked the nearside and this wasnt as bad, it seemed to work straight away no noise but its come back again, and its hard to show people as sods law determines it doesnt happen when you want it to, does anyone know what could be the problem?, theres no knocking noise its just a high pitch screeching type of noise (hard to explain).

Any help would be much appreciated

[paul.h]

Maybe it is an air leak in the vacuum pipework to the brake servo or in the servo or the vacuum pump. If so you may hear it under the bonnet with the car stationary and the engine running/revving to simulate the high speed.

[Luke]

Hi Paul, thanks for replying. sorry it took me a while to reply back, got a lot going on in my life at the minute to say the least lol, It doesnt happen when sitting still or even moving off slowly its as it picks up speed, which is rather strange, plus with the fact it doesnt happen all the time which is what really gripes me hehe.

[paul.h]

Does the noise go if you touch the brakes lightly with the left foot and keeping the right foot on the accelerator so there are no changes related to the engine such as the turbo ? Its just that whistling noises would normally be associated with air flows/leaks and lifting the accelerator pedal to go on the brakes affects not only the brakes. Whining noises could be bearings related and if a wheel bearing, the noise may alter when turning left or right. You could also try removing the wheel trims (if possible) in case these are giving a noise.