328i E36: whining noise when decelerating

[B234R]

Hi everybody, let´s see if you could help me with this issue.

My car is a 328i E36, manual, 130,000 miles. I´ve bought it one and a half years ago, it drank a lot of oil so last summer my mechanic put a second hand engine from a 1998 528i E39 auto, and a new Sachs clutch kit. This engine doesn´t use a drop of oil.

Problem is, since the "new" engine (and clutch) was installed, there is a whinning noise when I lift off the throttle. I know that trying to diagnose a noise it´s diffcult, but...

-It happens in every gear
-Always with the car in motion
-Only sounds when decelerating; if i´m accelerating it doesn´t sound at all
-The noise sounds louder depending on the engine RPMs
-If I push the clutch the RPMs fall and the noise is very low, although I swear it still sounds a little bit. If I put neutral it doesn´t sounds at all.
-When putting the engine and the new clutch my mechanic said the old dual mass flywheel was in good condition, so he didn´t replaced it. He changed the gearbox oil
-Gearbox works fine, clutch too

With the old engine (and clutch) there wasn´t any whinning noise. If there is a problem with the gearbox, I suppose the noise would increase when accelerating, wouldn´t it?

The noise is a bit annoying, not more. It isn´t worse now than a few months.

Any suggestions and experiences would be great...

Thanks!

[B234R]

I´m not very sure, but I believe it´s from the front of the car.

[B234R]

I don´t have a video but I´ll make one.

Engine mounts were replaced while the engine swap. I don´t see the engine moving too much with the open bonnet.

I´ve seen videos of layshaft bearing failure on youtube and the sound is different, and it sounds when accelerating. Mine only sounds when lifting off the throttle...

Thanks a lot!

[B234R]

With the A/C on the noise is the same.

When they changed the engine, the workshop told me that the swap was very straightforward despite being a M52 unit from an auto...

The fact that the noise is only present when lifting off the throttle makes me suppose that it´s not a problem from the gearbox, differential, etc...it could be an air leak somewhere. I´m going to tell the mechanic to remove the inlet manifold, and take a look for vaccum hoses. I´ll keep you informed.

Thanks!

[B234R]

Well, after removing the intake manifold it seems everything is right, so I suppose we´ll have to take out the gearbox and see what´s going on.

The car goes perfectly and the sound isn´t loud, but I´m very picky with car noises..

[B234R]

I don´t think it could be the engine mounts, they are new, and the whine doesn´t sound at idle, only in deceleration...
Before the engine swap the differential was silent.

I suspect of something screwed up in the engine/gearbox installation, I´ve just read some posts in a US Subaru forum where people complain about a whining noise when decelerating right after a clutch replacement in their Impreza WRX, the problem is a slight drivetrain alignment. I´m going to try pumping up the tyres in one axe and letting out air in the other and see if there is a difference.