[lawwailok]

i know there's been threads/posts about turbo siren. but i have a question here, let's say if the turbos are bad, and start making the siren sound. normally at which rpm it will occur? will you be able to hear it at higher speed ie: 40mph+?

and of course if they are really bad, you should be able to hear it at any gear, correct?

reason why im asking is because i do hear some kind of weird noise when im driving at slow speed, which is 30mph or less. it's pretty fainted noise, and i had my friend rev in the car to about 2000rpm+/-, we both hear that noise is somewhere near the airbox/alternator area. the turbo/exhaust mainfold side is completely normal. i do specially hear it when the car is moving from a dead stop with a light foot gas.

any help is appreciated!

[bigdnno98]

[QUOTE=lawwailok;10731184]i know there's been threads/posts about turbo siren. but i have a question here, let's say if the turbos are bad, and start making the siren sound. normally at which rpm it will occur? will you be able to hear it at higher speed ie: 40mph+?

and of course if they are really bad, you should be able to hear it at any gear, correct?

reason why im asking is because i do hear some kind of weird noise when im driving at slow speed, which is 30mph or less. it's pretty fainted noise, and i had my friend rev in the car to about 2000rpm+/-, we both hear that noise is somewhere near the airbox/alternator area. the turbo/exhaust mainfold side is completely normal. i do specially hear it when the car is moving from a dead stop with a light foot gas.

Waste gate rattle? YouTube 335i waste gate rattle. It'll let you know if that's what you're hearing or not.

[Ilma]

Unless it's your alternator, don't worry about it.....

A little bit of siren noise on low rpm turbo spool up is not uncommom.

Usually occurs between 1500-2500 rpm at light throttle input.

I experienced the same noise on two different sets of turbos and they ran fine.

If the noise gets noticeable loud and screech-like at all rpms....... then you have a problem.

[JamesM3M5]

Could be belt tensioner pulley or idler pulley going bad. They're just sealed ball bearings and will eventually make a whooshing/light scraping noise. Typically last about 50-75k before they get loud.

Alternators under load can also make a light noise.

[lawwailok]

Originally Posted by bigdnno98

Waste gate rattle? YouTube 335i waste gate rattle. It'll let you know if that's what you're hearing or not.

no, my wastegates are absolutely fine.. they are working like a charm, *touch wood* =)

Originally Posted by Ilma

Unless it's your alternator, don't worry about it.....

A little bit of siren noise on low rpm turbo spool up is not uncommom.

Usually occurs between 1500-2500 rpm at light throttle input.

I experienced the same noise on two different sets of turbos and they ran fine.

If the noise gets noticeable loud and screech-like at all rpms....... then you have a problem.

i usually only hear them at 1st, 2nd gear at light throttle and under 2000rpm, anything rpm higher, it's quiet

[lawwailok]

Originally Posted by JamesM3M5

Could be belt tensioner pulley or idler pulley going bad. They're just sealed ball bearings and will eventually make a whooshing/light scraping noise. Typically last about 50-75k before they get loud.

Alternators under load can also make a light noise.

is belt tensioner pulley/idler pulley a common problem on N54? the car is ~49k miles at the moment. and the noise has been noticed since a few months ago, and so far it's not getting any louder AFAIK.

[JamesM3M5]

Not really a common problem, just a possible maintenance item. If you can get a mechanics stethoscope, you can listen to the tensioner, idlers, and alternator bearings. Be careful around the moving belt, though.

[rader1]

Or if you can't get a stethoscope you can use a long screwdriver and touch it against the part in question and touch the handle against your ear. Doesn't work as well but it helps.

[blisstik]

Time for RBs!

[lawwailok]

Originally Posted by blisstik

Time for RBs!

no G, i couldn't hear anything from the turbo side... all those noises are around the airbox/alternator area...
LOL... good call tho on the RBs =)