Performance issue BMW E90 320d

[STAR89colin]

Greetings to everybody,
I own a 2006 BMW E90 320d with an M47 diesel engine.

I just acquired the clutch assembly along with the flywheel.

Shortly thereafter, I encountered an issue with performance and a humming noise that I can elucidate as follows: "When I accelerate in second gear and exceed 2300 rpm, upon attempting to shift into third, the rpm decreases as expected. However, when it reaches approximately 1800 rpm, I hear a humming noise akin to air being ground." This occurs during the shifting process as the rpm declines to around 1800.
It also occurs during gradual acceleration in second gear, when I can hear it as well.
One month later, I began to lose power until reaching 2500 RPM, at which point the vehicle accelerates flawlessly.
I replaced the air filter and EGR valve, after which the issue of power loss seemed to be resolved.
The previous EGR was obstructed by a wet carbon oil combination, despite having been cleaned three months before.

However, I now see that the issue is progressively reemerging, and the buzzing noise persists.

I own no error codes.

200,000 kilometres

No discernible oil leaks or depletion.

At high speeds, the automobile seems to function well; yet, it exhibits issues mostly in urban environments.

I apologise for the lengthy explanation.
Thank you in advance.

[BMW_Fan2020]

Are all the hoover pipes functioning properly?
Ensure the boost hose is correctly installed and free of any splits.
We need any trouble codes.

[STAR89colin]

No fault codes, which the boost hoses did not comprehend.

[STAR89colin]

I am uncertain whether this is relevant, however I replaced the water pump and thermostat when the vehicle had 180,000 km, one year ago. I have seen that when driving in the city, the coolant temperature remains about 90 degrees; however, on the highway, it drops to 70 or 65 degrees. I am uncertain as to why this occurs, but I understand that it should not happen.

[BMW_Fan2020]

Was the thermostat authentic, as it seemed to have malfunctioned once more?
The boost hose is the large conduit leading to the turbo intake.

[STAR89colin]

The thermostat originates from BMW.

[BMW_Fan2020]

Did you also replace the EGR stat?
It seems to be an issue with the thermostat.