pm101

Hi everyone,

2013 MB C250 4 dr sedan

I have a noise that has come up in the past few months that is driving me crazy. It's a buzzing sound that is coming from the front right of the car. It's heard when the brakes are depressed and the air conditioning system is ON. The sound is a constant noise with no variation no matter what speed the car is traveling nor the speed of the air conditioning fan. I must clarify my use of air conditioning as it's not just when the air conditioning is on but when the air handling system is on. Compressor being on makes no difference. Hot / Cold.. no difference. If the system is on and you hit the brakes, the buzzing noise will occur. turn the system off and brake, no noise.

This problem first started after a trip to the mountains with lots of winding roads which means brakes were used a lot. Also, the noise only occurred when turning. NOW, however, the noise is heard any time the car is driven. straight, turns, ...doesn't matter. noise is there.

I am puzzled because I do not see how these two systems interact with each other. I do know it is a very annoying sound.

Has anyone run into this or has any idea what could be happening? The dealer is at a loss to explain. Thoughts?

Thanks in advance. :-)
Nathan

alecmascot

Something is touching the blower fan blades ?

pm101

Hi, thanks for the reply.

Unfortunately, no. I did have the blower checked for debris. No joy.

Also, the sound pitch does not change with the speed of the fan/blower. It's a constant buzzing ..almost an electric buzzing sound that is only triggered when the brakes are applied and the air/heat system is on inside the car.

decorily

Does this sound occur if you depress brake pedal while car is stationary or only while in motion?

pm101

Thanks for replying and good question. i apologize for leaving that out of the OP. the noise is only while in motion. once the car is stopped, no noise. it can be in park, no noise. stopped at a light, foot on brake, no noise. only when in motion.