I was hoping for some help diagnosing a groaning noise before I send the car to the dealer.

Symptom:

After the car is warm, I get a loud groaning noise coming from the rear of the car (unclear whether left, center, right) on low speed (less than 10mph) full hard left and full hard right turns.

Specs:

Car: 2010 Porsche 997.2 Turbo
Mileage: 19K
Suspension Mods: Bilstein B16 Damptronic Coilovers
Wheels: RSVforged 20x9 front and 20x12 rears, 3pc wheels
Tires: Michelin Super Sport 245/30 front and 325/25 rears with 75% tread left
Last Alignment: about 12 months ago (within stock specs)
Stock Wheels: 19" Turbo II with Michelin PS2 90% tread left
Balancing: Aftermarket wheels are brand new (less than 1000 miles). They have never hit any kind of bump or pothole. They were run on a balancer last week and were perfectly balanced. Stock wheels were also run on a balancer just in case and were also perfectly balanced.
Diameter Difference: Negligible difference in diameter between stock and aftermarket wheels as it was sized specifically to maintain the same overall diameter
Weight Difference:Each aftermarket rim is about 6lbs heavier than the stock wheel
Width Difference:Stock rears are 11" I believe and the aftermarket wheels are 12".

Testing Done:

Car with aftermarket front wheels and rear wheels exhibits the noise. Replacing the rear wheels with stock wheels eliminates the noise. First thought was something's wrong with the wheels.

I marked the after market rear wheels "A" and "B" so I can identify them. Here's a table of various combinations I ran to narrow down the issue:

Wheel A (driver side) + Wheel B (passenger side) = NOISE
Stock (driver side) + Stock (passenger side) = No Noise
Stock (driver side) + Wheel A (passenger side) = NOISE
Stock (driver side) + Wheel B (passenger side) = NOISE
Wheel A (driver side) + Stock (passenger side) = No Noise
Wheel B (driver side) + Stock (passenger side) = No Noise

When building this table, I drove the car while attempting repro after repro. The NOISE cases all exhibited quickly and were very reproducible. The no noise cases were after attempting repros for 10-15 minutes each time.

After building the table, there does not seem to be anything wrong with the aftermarket wheels (again they are brand new) as the wheels did not exhibit the issue when mounted on the driver's side. It seems like however the aftermarket wheels are exposing some type of issue on the passenger side rear.

It is clear the noise is coming from the rear. It is not clear however which side of the car the noise is coming from as it seems equally loud on both the left and right sides of the car.

I checked for fender rubbing via chalk and painters tape, and there's no rubbing. The wheels are clearing everything on the suspension and not rubbing. Inside the wheel I see no marks (inner barrel) where some type of rubbing would have occurred. I see no rubbing marks on the tires either. No black streaks in the wheel well plastics or body or suspension parts.

I was wondering if it could be a wheel bearing but I'm told 19K miles is way too early for a bearing to go. I also did the wheel pull test to check for slop and found none.

I was thinking perhaps the wheel on the passenger side rear could affect the amount of effort required to steer the car? So perhaps it's the steering? I checked the power steering fluid level and it seems fine. Perhaps the steering pump? But not sure how I can check the pressure or if the pump is the issue?

Not quite sure what else it could be. If anyone has any further ideas on what I can check, I'd appreciate some advice.

Here's a video of the noise. From the video, it does not sound like a rubbing noise. It sounds very mechanical. The noise is rotational and I can feel a slight vibration inside the car / on the steering wheel when it happens. If I stop mid turn, the noise stops. It's tied to wheel motion / car movement. Anyhow, here's the video:

 

Sounds like it might be an issue with your differential

 

I was thinking the same thing. If the sound is certainly coming from the rear, it could be the LSD or transmission.
Check your output seals and trans fill/drain plugs.

 

Thanks guys. I guess I will have to have the dealer take a look. My CPO should cover it. I just wanted to rule out the wheels and suspension first since they are aftermarket. I don't think they are the cause. Don't see how they could make that noise given the tests I have already done.

 

I decided to try lubricating the suspension bushings. I started with the drivers side because I thought I heard a slight creaking at the end of my tests yesterday on that side. I lubricated all of the bushings including sways. After just the driver's side, I took it out for a drive. I can't repro the noise now. Spent about 45 minutes trying to repro and cannot. I'm going to keep listening for it for a few days and see if it comes back. If it doesn't or if it takes a while to show up again, I'm guessing perhaps one of the bushings is going bad or has dried up after 5 years?