Quote:
Originally Posted by pikcachu
usually just re-torquing the wheels fixes it...it can also be the brake shield
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For me, torquing the wheels has no or little effect.
I have my own theory about this. I don't think it's wheel bolt torque, or micro slipping of hub surfaces. Here's my chain of events and my reasoning.
I recently discovered that it is affected by tyre pressure.
Both myself (M240i) and a colleague (M2) experience this ticking sound. We both only get it with summer tyres, he has had the hubs cleaned and friction plates installed according to the service bulletin. He still hears it occasionally, a year or so later.
For me it started (or was noticed) after a hard track session. I had mounted Michelin Pilot Sport Cup 2 tyres a couple of years ago, with a 10mm front spacer and noticed the sound when leaving the track, noted it, but didn't think much of it. I pumped up the tyres to street pressure for the ride home and completely forgot about it.
I run at ~2 (30 psi) bar on track, ~2.4bar (35psi) for daily driving.
While testing and bedding new brakes the next summer, I reduced the tyre pressure to boost grip in some warm weather. The ticking sound was very apparent and triggered a frenzy of testing, torquing, and arguments with the dealership which resulted in no conclusion. I could not figure it out. I did not make the connection with tyre pressure.
Around that time I mounted M2 LCAs, (only, no TS) removing the spacers. Still ticking. I drove for a few weeks before switching to winter tyres. The ticking sound disappeared.
I had at this stage gotten used to it.
This year, when I switched back to PS2s for summer, I was not even thinking about the sound. It was completely gone.
The place where I store my tyres over winter had pumped them up to 2.6 (38psi) bar cold. I think they do this for fuel economy reasons. I saw this when I reset the tyre monitor, but could not be bothered to reduce the pressure, I only had short trips to do.
As the weather improved and I got more focused on driving again, I finally dropped the pressure to a more appropriate 2.2bar cold.
On the very first corner, tick tick tick tick tick tick tick tick...
My purely speculative theory is that it is related to front grip. I think the DSC or ABS unit is activating when the wheels turn at different rates. When the grip is low, like with thinner winter tyres, or the tyre patch is smaller when the tyre is pumped up, I don't think the DSC/ABS unit needs to work as hard if at all. The ticking sound reminds me of when you trigger ABS and lock up the front tyres, it pulses at a similar frequency. My guess is that the DSC unit is doing something with the brake lines, similar to the way the brakes are pretensioned if you let off the gas suddenly.
There might be a way to affect this with coding thinking about it.
That's how I see it. Not wanting to spread misinformation, but this issue quite literally has no known solution, service bulletin or not, so I don't feel bad throwing out another hypothesis.