New to the forum. I have an '03 E85 2.5i roadster with 130k miles. Ever since I bought it a year ago, it's been making this high-pitch whining noise intermittently. Seems to be getting worse in the last couple months. It only appears when the engine is warm, usually after 20 or more minutes of driving. It is monotone and I can only really hear it at low speeds or when idling. Easier to hear from inside the cockpit. The instant I step on the brake pedal, the noise stops and then when I lift my foot off the brake it creeps back to full volume in about 2-3 seconds. When I put my foot under the brake pedal and pull up, providing upward pressure on the brake pedal, the whining gets louder. When I shut the car off, it fades out over the course of 3-5 seconds. I took it to a local German vehicle mechanic and he wasn't able to identify the source of the sound (but he did convince me to replace the DISA valve). Because it is so high-pitched, it's near impossible to tell exactly where it is coming from. Anyone have any idea what the heck this is and how I can make it go away? I don't notice any mechanical issues stemming from it, but it sure is annoying. I find myself tapping the brake pedal repeatedly at low speeds just to keep the whine at bay.
High-Pitch Whine
- Thread starter Pirish
- Start date
A good chance others will have heard similar.If it's noisy when at standstill, sounds louder inside the car than outside and disappears when you touch the brakes, then that's classic symptoms of a a leak in the brake booster line or diaphragm. When static remove the booster vacuum pipe at the booster to see if noise changes (but don't drive like that!).
I'd also be getting up close to check the ABS pump which can buzz/whine, then stop when brakes are applied (this would be the ££££! at BMW, but there are reasonable ABS pump rebuild services now). Check for fault codes with a cheap bluetooth OBD2 diagnostic and app like TorquePro.
Lastly check for a defective engine crankcase breather, touching the brakes changes pressure in the engine breather circuit when the brake booster vacuum changes. A collapsed breather pipe would be an easy first sign to look for, otherwise removing and examining the system for blocks/leaks is needed.
Do let us know how you get on
I'd also be getting up close to check the ABS pump which can buzz/whine, then stop when brakes are applied (this would be the ££££! at BMW, but there are reasonable ABS pump rebuild services now). Check for fault codes with a cheap bluetooth OBD2 diagnostic and app like TorquePro.
Lastly check for a defective engine crankcase breather, touching the brakes changes pressure in the engine breather circuit when the brake booster vacuum changes. A collapsed breather pipe would be an easy first sign to look for, otherwise removing and examining the system for blocks/leaks is needed.
Do let us know how you get on
Hi Pirish,
I've had similar issues but I've noticed it mostly after I've filled the tank up. Fuel pump issue in my case I think.
Not sure if this is the same thing, but I've followed threads where people have spent huge amounts of money trying to sort these things out without success.
I've just got round to living with it. It hasn't got any better, but it hasn't got any worse either
Robert
I've had similar issues but I've noticed it mostly after I've filled the tank up. Fuel pump issue in my case I think.
Not sure if this is the same thing, but I've followed threads where people have spent huge amounts of money trying to sort these things out without success.
I've just got round to living with it. It hasn't got any better, but it hasn't got any worse either
Robert
Fair point, the whining sound I hear is always after I've filled the tank up and thereafter when the engine is idling. Once the tank is about half full or less, it gradually dissappears. After nearly five years of ownership, the symptoms haven't changed, so I've decided to live with it. But nothing to do with braking all the same.
Chickendippers
Member
Mine was more of a screech but similar sounding issue. As another poster has recommended, check the crankcase breather as it gets clogged.
Ewazix said:
I think I know what the brake booster line looks like. (circled in red in the photos). Does that look like the right hose? Want to make sure before I start disconnecting things willy nilly. Hard to tell if I need to remove the hose clamps or if I can just yank the connection straight out of the booster.
Pirish said:
Is the noise coming from the booster and stopping when an assistant touches the brake? This should give you a good clue.
If you are not confident don't mess with brakes, but if you want to double check you should be able to pull the non-return valve out of the rubber grommet on the booster, if you have original BMW hose clamps they are very difficult to remove and need replacing with a special tool.
Note the instructions on BMW TIS to stop engine then pump the brake pedal a few times first to relieve pressure before disconnecting
Then you can re-start and see if the noise stops.
Stop engine again before re-connecting and ensuring all is sealed tight.
Don't drive with it disconnected.
Another quick thing to check for anybody with fuel pump or tank related odd noises is to check the condition of the fuel cap seal. The system relies on a balanced pressure so a defective seal (or loose cap) can cause noises and uneven running, sometimes with fault codes. I've just changed the seal on mine. see topic https://z4-forum.com/forum/viewtopic.php?f=3&t=125144
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Ewazix said:
I disconnected the hose and started the engine - It started idling rough and the disconnected hose was hissing very loudly which made it impossible to hear the whining noise. Prior to this, I had someone apply upward pressure on the brake pedal to make the noise louder and I was able to narrow it down to either the booster or the hose. Fairly certain I have a pinhole in the booster diaphragm; the hose looks ok. Aside from the noise, is there any risk/damage incurred from letting this go? Not sure I want to spend the money replacing it just yet as I just replaced the DISA valve with new OEM one for $$$.
Pirish said:
I'm glad you seem to have narrowed it down to the booster diaphragm, as I said at the outset your symptoms were as expected.
Nobody is going to say it's OK to drive with an under performing brake booster, if it failed completely you will have unassisted brakes and you will not stop in time, guaranteed. Truth is that a complete booster failure is rare, but as the leak gets worse your brake pedal may start to feel more solid which is the next warning after noises. Here in the UK knowingly driving with defective brakes that cause a fatal for example, will get you serious jail time, personally I'd rather have my pants pulled down at the BMW parts counter than in the jail shower block.
This is why I try to avoid the BMW parts counter at all costs.!!! Never know what you might see!!!!Pirish said:
No problem (excuse the Brit' humour :wink: ).
I would double check the booster one way valve before committing to a replacement booster unit, a simple inspection and blow/suck test will tell if it's operating OK.
I've fitted a used servo booster from a breaker before on other cars I've owned and not had a problem which is obviously a lot less expensive, but would probably go for an aftermarket item at about half the cost of the BMW unit e.g. from a maker like ATE who make components for BMW. https://www.rmeuropean.com/Products/34336779681-MFG4.aspx
You can find the part number on Real OEM here https://www.realoem.com/bmw/enUS/showparts?id=BT33-USA-10-2002-E85-BMW-Z4_25i&diagId=34_1291
Good luck sorting it