Magnet Coil BKV: Error Code 00812 Troubleshooting

Hello my specialists,

Unfortunately, I'm having another problem with my little darling .
Golf 4 TDI AJM.
Year: 1999, with ESP.
77,000 km on it.

First, let's talk about the background:
I installed winter tires on the car on Saturday, raised the suspension (using adjustable coilover sleeves), and installed new strut mounts.

"On Monday morning, as I was driving to school, the ESP light suddenly came on when I was halfway there. In the afternoon, the light was off again, and it hasn't come on since!"

Okay, today I finally hooked up my VAG-COM / VCDS, and it gave me the following error codes:

00812 - Solenoid switch for brake pressure (F84).
35-10 - - - Sporadically

00852 - Front speakers.
36-10 - Interruption - Sporadic.
00853 - Rear speakers.
36-10 - Interruption - Sporadic.

It seems like all the speakers are working, though.

I also had a new brake pedal switch installed about 1-2 months ago because the engine light was on frequently. Also, in the last few days, I've noticed a strange whistling sound when the car is cold, especially when starting in first gear.

"I thought that was the turbocharger, but it sounds different somehow?"
Can someone help me and offer advice?

Hi, I'd be very interested to know how you solved the problem or what steps you took next, as I'm experiencing the same error.

Best regards,