sqeaky mastercylinder/brakebooster

Does anyone else have a sqeaky mastercylinder/brakebooster? Everytime I press the brakes while going slow I hear a sqeaking noise that I thought was coming from the linkage in the brake system but after spraying lube on everything and further troubleshooting I determined that it's actually coming from inside the mastercylinder/brakebooster assembly. I bleed my brakes and the noise when to about half of what it was but its still there. I use to not have any noise at all. I checked a friend of mine's truck and his is doing the same thing and it also is driving him crazy. Is anyone else in the same boat and did you fix it?