I think I blew the head gasket on my rear right tire...

[heinzboehmer]

Okay, battery cable is fine, so that's good.



Drove the car some more and the noise is now showing up at lower speeds too. Also realized it's directly correlated with how much rasp is being produced by the engine, so I'm leaning towards the "something rattling around" theory. Will check out the underside of the car later tonight.

[bigjae46]

I'd check the parking brake cable isn't coming into contact with the axle. Sounds like it could be a wheel bearing, hub, axle or diff bearing issue. I'd look at the axle and make sure there is no evidence of something making contact. Then I would jack up the rear and spin the tires.

[heinzboehmer]

Quick update on this.

The airbag light came on the other day so I checked for codes with INPA. There was one code stored for some fault with the BST. Turns out that the BST connector is a bit broken and was only plugged in halfway. Plugged it in entirely (I'll swap it out soon), cleared codes and the light went away.

Next time I drove the car, the noise was gone! I was unable to reproduce it no matter how much I tried. Kinda sketch that it might have been related to the BST, tbh.

However, I hadn't driven the car since I took the rear interior apart to check on the battery cable, so it's totally possible that there was something loose back there and I accidentally fixed it when reinstalling everything. Don't think I'll know for sure, but the noise is definitely gone now.

[sapote]

Quick update on this.

The airbag light came on the other day so I checked for codes with INPA. There was one code stored for some fault with the BST. Turns out that the BST connector is a bit broken and was only plugged in halfway. .

Do you mean the small cable with the yellow connector, not the big module in series with the red cable? Does the cable have any sights of overheated around the BST?

[heinzboehmer]

Yep, the one with the yellow connector. No signs of overheating or sparks or anything like that.

[Casa de Mesa]

Can I ask a no flame question in the non-no flame thread?

What is BST?

[heinzboehmer]

Battery safety terminal.

It's an explosive "fuse" controlled by the airbag module that disconnects the battery from the starter and alternator in the event of an accident. It's that bulky thing on the positive battery cable.

https://bimmerscan.com/bmw-battery-safety-terminal/

[Casa de Mesa]

Battery safety terminal.

It's an explosive "fuse" controlled by the airbag module that disconnects the battery from the starter and alternator in the event of an accident. It's that bulky thing on the positive battery cable.

https://bimmerscan.com/bmw-battery-safety-terminal/

Wow, learn something new everyday! Thanks for that.

[sapote]

Wow, learn something new everyday! Thanks for that.

So now just in case a KGP agent kidnaped and locked you in your M3 trunk, you just pull that little wire (keep it connected to the yellow connector on the BST) and short it to the battery 12v and this will blow open the BST and the car will slowly die. The KGP can't figure out as the dash lights all still working fine.

[Casa de Mesa]

So now just in case a KGP agent kidnaped and locked you in your M3 trunk, you just pull that little wire (keep it connected to the yellow connector on the BST) and short it to the battery 12v and this will blow open the BST and the car will slowly die. The KGP can't figure out as the dash lights all still working fine.

Ha! I'll keep that in mind. Chances of me being stuck in my trunk are more likely due to my own doing, but you never know.