Odd power steering issue

Our lovely 996 has developed a strange steering issue. Nothing major but I'd like to deal with it before it becomes a real problem. Every now and then, the car pulls slightly to the right. It doesn't feel like a misaligned wheel, rather it feels as if the power steering is pushing it that way, and when turning the steering wheel back the power steering seems to fight back a little. It's not a strong pull and it only lasts a second or two, but it's there. What could this be?

Loose belt? Low fluid? Sure it isn't a crowned roadway? Tire pressure?

Loose suspension, steering linkage?

Steering Angle Sensor recalibration needed? This thread from 2010 talks about it: Steering Sensor calibration finally working on durametric. Mr. Owen and I have been working on getting the steering sensor calibration working on the durametric for the past few weeks. I emailed him a few months back stating it wasn’t working, and he asked me to data log the problem for him. I got really busy and I forgot about the issue but about 2 months ago Mr. Owen emailed me asking me if I had gathered the data he asked me. I told him I had not, and coincidently one of the forum members who had just acquired his 996 Turbo local to me was having psm/steering angle sensor problems. So I data logged quite a bit of files to Owen, and a few weeks ago he emailed me back stating it should be up and running. Well my car was perfectly fine, so I figured I would be the test mule to see if it works, and sure it enough, it disc librated up my steering sensor. So I had to go to Ace hardware and buy an angle locator to know how to calibrate as the it ask you to turn the steering 20 degrees each way. I tried guessing 20 degrees, and its best to just buy the tool. I went ahead and bought the tool. I got home and gave it a try: here is how it works. I would suggest to have a friend for assistance. Step 1) Turn on your car Step 2) Plug the durametric to the obd2 port. Plug the USB to your computer Step 3) Run the durametric software Step 4) Select your vehicles criteria, for 996 tt owners, 7.8ME and ABS 5.7 Step 5) Go to ABS 5.7 Step 6) Go to command. It will prompt you the steering calibration screen. Step 7) Drive to a parking lot where you know where straight is on your steering wheel. Run the car in a straight line until you know that’s ‘straight’ for your steering. Step 8) Stop the car without moving the steering. Step 9) Put the angle locator in the middle of the steering wheel, and adjust the angle locator to 0 degrees. Note: do not move the steering wheel. Step 10) Hold angle locator with both hand while holding the steering wheel, make sure it's reading 0 degrees Step 11) Have your friend press start calibration, and click ‘ok’ when the screen pops up. Step 12) Turn steering 20 degrees left and then right, then return to 0 degrees, all while holding the angle locator with both hands and turning the wheel. Step 13) Shut down the car, remove key and exit the durametric. If it’s still not 100% right, redo it and it will get better from my experience. Here’s how the angle locator looks, my steering is not straight as you can tell .

Tires, suspension are ok. There's no play in the steering linkage, and we've had the car aligned a month ago. Fluid is topped up, I check it regularly. If it were any of those, we'd feel it a lot more often or even continuously. This only happens maybe 2-3 times on every trip. It also doesn't feel like a crowned road surface. It's hard to describe, but it had too much of an "active" feel to it for that.

Thanks for the tip fpb111. The sensor calibration process is worth a try, or maybe the sensor itself is faulty.