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2000 BMW E46 323i
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Discussion Starter · #1 ·
Hi all, i'm curious if anybody knows the culprit of this. Since i got my E46 323i there has always been a weird audible sound. I cannot identify where exactly this comes from but sounds like it's somewhere under the steering wheel or inside the dashboard behind cluster gauge panel or similar. It's as if a pressure builds up and then suddenly but slowly releases. This happens mainly when there's cold outside but i think also in summer but not as audible as in cold. This happens a few times in a row and after 3rd time or so it goes away until the next day. It's most audible when i start the car and rolling away and shifting from 1st to 2nd in low rpms and cold engine. The fact is that car works flawlessly and this sound was present from day one of my ownership, but this didn't go away after a year and almost 45 000 kms. Anyone got idea what this is?
 

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2000 BMW E46 323i
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101 Posts
Discussion Starter · #3 ·
Hmm i assume that this would lead to worse braking effect or what? If yes than no, my car brakes feel very nice and it stops like it should.
 

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How's the AC working in there? If there is more than miniscule in the AC line it will freeze the expansion valve on start up & completely overwork your compressor. Most sensors won't indicate because they sense low pressure (low gas) situation but not the high pressure of a moisture freeze at the . That If and when the expansion valve DOES unfreeze ... or if the car (or you) turn off the AC .. there will be a quick rush of R134 , and you will hear that. try unplugging the compressor and see if the problem disappears. That's all I got .. (and I got nothing)!
 

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2000 BMW E46 323i
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101 Posts
Discussion Starter · #6 ·
How's the AC working in there? If there is more than miniscule in the AC line it will freeze the expansion valve on start up & completely overwork your compressor. Most sensors won't indicate because they sense low pressure (low gas) situation but not the high pressure of a moisture freeze at the . That If and when the expansion valve DOES unfreeze ... or if the car (or you) turn off the AC .. there will be a quick rush of R134 , and you will hear that. try unplugging the compressor and see if the problem disappears. That's all I got .. (and I got nothing)!
Well the AC doesn't work since day one of my ownership. I run the car without AC compressor belt. Could be the problem, i'm just not familiar with AC systems, all my cars had them faulty hahah. But i think i'm gonna rebuild the whole AC because i would like to have fresh system altleast for once in my car. Maybe then we will find the source of that sound.
 

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2000 BMW E46 323i
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101 Posts
Discussion Starter · #7 ·
maybe just the echo noise from the SAP pump turning off.
I don't have SAP in my car, but some other guys also pointed this out. I waa searching around various forums and found out that the closest sound to mine that the others had is brake booster related problems. But mine is fine, it holds vacuum for some time and while sittin overnight, the next morning the pedal is half way soft, not very hard to press. Idk, i was just curious what it could be. Tried to find out something with local E46s, but none had this, nor my friends 330xd had this.
 

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I have one other idea. Try removing the oil cap with the engine running, and see its its really really hard to turn & lift off.
 

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2000 BMW E46 323i
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101 Posts
Discussion Starter · #9 ·
I converted to oil catch can so my engine is under a bit higher vacuum than with original CCV system but this hissing sound was present even before the catch can install and it didn't change. Thx guys for your input i think it's brake booster related but again, i didn't notice anything unusual. All my cars before had similar pedal feel and i know they were OK.
 
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