The only time I have noticed engine whine noise, is sometimes when the car also has an alpine amplifier upgrade.
The engine whine can happen with a stock Bm54/53 as well.

Alternator and battery can also have an influence. When the Bm54/53 is in stock form, it drains less power. With the amp kits, it uses more power.

Out of the 1000s Bm54/53 units I have done, I’ve had about 3 people with engine whine issues.
The original poster.
Someone who came back to me and we put original untouched unit in his car and still the same engine whine.
And a current one, who had the engine whine issue before sending his unit to me and still has it afterwards.

All 3 with X5s. So could be an x5, alpine amp, or some other electrical current issue somewhere else in the car.

Eventually all the Bm54/53s will be upgraded/repaired, as they all start losing channels, especially in X5s.

Any other questions do let me know.

Ps. Can upgrade the firmware on both Bm54 and bm53. Also upgrading Bluetooth ULF units to generation 13.

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