Rotational squeak from left rear... unable to diagnose

Asking all the S550 groups this...

I have a 2015 GT PP. The OEM brake pads are noisy as we all know, and they were squealing pigs all the time. I switched to G-LOC pads and resurfaced the OEM rotors (i only had around 7k mi on them at the time) in hopes of solving the issue, and all was good for awhile, but lately (@10k mi)I've started experiencing a rotational squeaking noise from the left rear that goes away when the brakes are applied. It takes about an hour to start making noise, or after being driven and parked for a certain period of time.

Since then I've tried several things, such as resurfacing the rotors again, switching back to the OEM pads, and even replacing one rear rotor with a new one (left side), but the squeaking remains.

Has anyone experienced this before? Someone said wheel bearing, but the last time I had a wheel bearing fail was in my old Subaru WRX and it was more of a rumbling sound than a squeak?

Could it be the differential? :'(

Thanks in advance...

How much aggressive driving does the car see? Got pics of the pad surface (are they glazed?)

You mentioned that swapping pads fixed it last time, well indicates that the noise is indeed pad related and not something else like a hub.

The GLOC street pad will squeak a bit if you drive the car hard and get even the tiniest bit of glazing. If you track it and glaze it real good, it can squeal like a banshee. Take the pad off and hit it with some 80 grit sandpaper and see if the noise is reduced. That fixed my GLOC rear street pad noise issue. You can also apply some anti squeak grease to the slider pins and pad backs, but dont expect much from that, its probably the pad surface which needs working over.

Generally, on our cars the left/drivers rear hub will go out first before the right/passenger side. If both are squeaking its probably pads not the hibs.

Pull back on the brake rotor tin shield to give it more air space from the rotor. Go for a drive. Hear the noise?

i unfortunately did not photograph anything as it was at the mechanic's and i did to want to be in the way as he was on the clock and could only watch from the bay door.

the dust shield was one of the first things checked and it's not making contact, but the mechanic did not bend it back any more than where it's at now...

we switched from the g-locs back to the oem pads and the noise continued on uninterrupted after the change. the mechanic said the pads do not show glazing (i do not track the car daily driver only), and he did sand them down as per procedure, but he wondered why g-loc has a larger pad profile than oem and if it was a possible cause, but he dismissed that after the squeaking continued with the oem pads going back in.

again it's a rotational squeak while in motion at any speed, which stops when the brakes are applied. this is from the left rear.

have you tried the anti-squeek spray on the back of the pads?

melwff said:

have you tried the anti-squeek spray on the back of the pads?

Click to expand...

We used Brake Quiet from Würth. made no difference.