Annoying wheezing or whooing sound between 750 and 1250rpm
Dear members, I hope someone can help to identify the issue I am having. I am hearing a wheezing or "woooing" noise only when the vehicle is at around 750-1250rpm, both accelerating and decelerating. Over 1250rpm the noise just disappear (I think it's masked by the regular engine sound). It's more noticeable especially when the vehicle is decelerating as the engine quiets down. I have changed numerous parts hoping to fix the problem with no success. Below are what I have replaced,
- Lower and upper intake boot
- Tensioner pulley
- Idler pulley
- Alternator pulley
- AC belt
- Serpentine belt
- water pump
- replaced spark plugs and air filter
- DISA removed and inspect and found working properly
This problem was first noticed about 3 months ago after my mechanic topped up the freon. I switched both the A/C and air circulation off and the noise still can be heard. It tells me it's not the AC. The AC makes it a little louder at times but it's not the root cause.
I brought the vehicle to a couple reputable local Bimmer shops and the mechanics told me the noise comes from when the alternator recharges and it's normal. I am not convinced because I have driven other 325xi without the noise. Also, if the noise is normal I wouldn't think anyone would have bought a bimmer to begin with. It's not super loud but without turning the radio or music on you can definitely hear it.
I seem to have done everything people suggested from different forums but the root cause is still not identified Please, I love my bimmer and I hope some knowledgeable folks can help.