My son who lives about 100 miles from me has a 94 honda accord. Some time ago it started intermittently making a noise when the brakes are applied. It is not a brake pad feeler warning noise. It is what I would describe as at hum or tone somewhat like you would hear from a pitch pipe. It will make the noise when the brake pedal is depressed even when the car is not moving. I thought at first it might be a vacuum leak but I think the length of time it is emitted would rule that out. I think it is more likely electronic. I put a stethoscope on the master cylinder and could detect it there but it may be actually coming from elsewhere, maybe even under the dash. I should mention that the car does not have ABS. I am not that much of a mechanic but if I knew the source I think I could remedy it. This really has me buffaloed. Wondering if anyone has experienced similar problem or have any ideas? brakes seem to work fine but I don't like not knowing what the sound is. Son has been asking what noise is all about. Thanks for reading this and for any suggestions.

 

I've moved this.....please read the notes in the DIY Section. Things like this belong here (General Tech).

 

There's a fair amount of vacuum stored in the brake booster. Turn off the engine & press the brake pedal repeatedly to see if it "runs out" of vacuum after awhile.

 

Thanks for the tip. I don't have the car right now but will try it when I get it. Any other suggestions appreciated. thanks again