"Low Humming" Sound when Air-Cond on.

[tank34]

Gents, need some help trying to identify a problem with E46 325i (2003, 90+k's). I hear a low humming sound especially when the air conditioner is turned on. When I was a kid, I used to ride a bicycle fitted with a little dynamo that powers up the bicycle lamp, and it sounds similar to that. When you turn off the air-conditioner, the noise goes away, so suspect it is either fan belt, or some sort of tensioner. The sound is more audible inside the car then outside. I've gone through the forum and someone has suggested that it could the alternator, but like i said, only comes on when the air-cond is turned on. Any suggestions?

 

[affan66]

if it is coming from inside the car, most likely it is the aircond blower motor. Costly to replace but there might be places that can service the motor/bearing.

 

[tank34]

Hi affan66,

I took the car to Naidu last week and the blower seemed fine. I have a suspicion that it could be the "Alternator" due to the sound be emitted, what is the possibility of it coming from there?

 

[affan66]

the sound is louder from the interior or the engine compartment?

 

[Lee36328]

In my case, I found some a buzzing noise caused by the fan of the ECU.

 

[jarance]

Hi affan66,

I took the car to Naidu last week and the blower seemed fine. I have a suspicion that it could be the "Alternator" due to the sound be emitted, what is the possibility of it coming from there?

If it the alternator sound, the low humming sound will still be there whther the
aircon is ON or OFF cos the alternator is always turning when the engine is running.

The sound could be noise from the radio as it tends to pick up the alternator
noise. off the radio and "see" or "hear" whether the sound disapper.

Yes aircon AHU motor being inductive load can generate noise. The noise can be eliminated or reduced via capacitor (suppressor).

 

[bmw7833]

In my case, I found some a buzzing noise caused by the fan of the ECU.

Uncle Lee, u can take out the fan thingy mah..The sound sure eliminated..

 

[tank34]

Hi Lee,

I will check out the ECU fan (if there is one for the E46).

Affan, the noise is a little more audible inside the cockpit, and it does pickup when you accelerate from a standstill. However, once you exceed abt 40km/h, the noise just goes away. A couple of things, when you exceed 40km/h, the louder engine noise can drown out this noise. Also, if it is fan related, the noise should not increase when I accelerate, which led me to suspect it could the alternator. However, not forgeting the noise does go away completely if I turn the airconditioner off (the engine still on and running of course).

Ken.

 

[TTang]

humming sound is what note A B C D E F G

 

[Lee36328]

Uncle Lee, u can take out the fan thingy mah..The sound sure eliminated..

Yeah, but the ecu will die faster from overheating, in which case, the next noise will be me screaming...

Hi Lee,

I will check out the ECU fan (if there is one for the E46).

I think so; all ecu comes w a fan to disperse the heat.

Affan, the noise is a little more audible inside the cockpit, and it does pickup when you accelerate from a standstill. However, once you exceed abt 40km/h, the noise just goes away. A couple of things, when you exceed 40km/h, the louder engine noise can drown out this noise. Also, if it is fan related, the noise should not increase when I accelerate, which led me to suspect it could the alternator. However, not forgeting the noise does go away completely if I turn the airconditioner off (the engine still on and running of course).

Ken.

Ken,

I had some noise previously, which I could not be sure whether it was coming from the alternator or power steering pump. My highly precise scientific method was this. I took a broom stick, and put it on the alternator with one end of the stick, and pressed my ear to the other end of the stick and listened. You'll be amazed at the slush-slush-slush-chug-chug-chug noise you can hear. Next, I did the same to the power steering pump. Confirmed, alternator sounded harsh, and duly replaced. Car very quiet now.

I call this the Broomstick Test Procedure. The workshop does the same thing, except using a stethoscope.

 

[bmw7833]

Yeah, but the ecu will die faster from overheating, in which case, the next noise will be me screaming...

I dun know about this..Thkx for the information.

 

[pussy]

As for me, dun bother.. cos the sound will be heard before 40km/h...

if you are fussy, most of the parts you will change to find the source, more $$$ will be spent..

for instance, i had this funny sound coming from the front, sounded like a grinding metal, tot it was the compressor, alternator, power steering, ETC... could not trace it for weeks... so i let it be for a while till something gave way... dun worry, you will notice it.. so it was my electric fan..

 

[bmw7833]

Dun lar fussy like Mr.M..U will feel painful when u want to change all the small thingy part..

 

[tank34]

If it the alternator sound, the low humming sound will still be there whther the
aircon is ON or OFF cos the alternator is always turning when the engine is running.

The sound could be noise from the radio as it tends to pick up the alternator
noise. off the radio and "see" or "hear" whether the sound disapper.

Yes aircon AHU motor being inductive load can generate noise. The noise can be eliminated or reduced via capacitor (suppressor).

Hi Jarance, it's definitely not radio related since I have to turn it off to actually here it. Am planning to send it to Naidu this weekend. Question, what is usually involved in an air-condition service. Naidu told me that in addition to gas top up, he wanted to replace the air-cond gas filter (about RM300), not too convinced about that.

 

[devilsadvocate]

bro tank34,

i'm having the same prob as your with my e46 - 2002. Did the ac gas filter replacement solve the problem?


cheers

 

[tank34]

Devilsadvocate, have not done anythin to the a/c yet. The noise persists but I do not have any idea what is causing it. I really doubt changing the gas filter will improve things. I suspects one of the bearings could be the problem.

 

[devilsadvocate]

Oh Ok tank34,

the noise is now unbearable and plan to visit Mr.Naidu for a second opinion as my usual mech insists that the compresser is gone.

cheers

 

[Vincent Hor]

M50 engine has this common problem with the Air Cond tensioner. Try to check this and the belting too.

 

[BMW6161]

bro tank34,

I'm having the same problem as your with my e46, sound gone after i change the belt tensioner it cost me $380

 

[devilsadvocate]

bro bmw6161,

where did yo change the belt tensioner?

cheers