Brake system problem in a renault megane

Hello everyone, I have a problem and I need someone to make me a hand if possible: I have a Renault Megane Sportway Coupé of the year 2002, which, except for some setback with the injectors shortly after buying it and the electric windows recently ago, the truth is that it has behaved very well, until now. It turns out that many months ago, he began to do like a whistle (a kind of "fsssssssh ..") that was initially mild but that over time it has become almost unbearable, from the brake pump, in fact, when stepping on the brake, the "blowing" disappears, sometimes it also stops doing it in some accelerations, but every time it remains longer, I also notice that I notice that I notice that it goes up when I This, I took him to the brake workshop and changed my records, the pills and reviewed the entire system, they told me that the blow was due to the fact that a brake pump joint dilates with the temperature changes but that in principle does not affect the braking, in fact, it slowly stops, they said that it would be solved by changing the pump, but that it prepared about € 500 .. !! Please, if Algien could give me a solution, I would be forever grateful. Greetings and a hug to everyone.

Hi: Look at the brake pump serve (which looks like a flying plate), a vacuum retention valve is connected (it is similar to a headset). This valve is usually economic, and when it breaks, it usually emits a whistle, which is nothing more than empty that escapes by this broken valve.
The number of this piece is 7701206228.

Greetings from Cordoba, Argentina.