When 2 days ago I noticed the humming noise, I pulled over and checked the tire pressure and they all had 35psi. Looked under and noticed wires sticking out of the rear tires. Today I replaced them with 2 new tires, but the humming is still there. The tire person said i might need the fronts replaced also, but the fronts look ok.

Anyone experience humming noised on the 996? I did a google search and it comes up with humming noised related to bearings. It's really hard to tell where it's coming from, since it radiates through the whole cabin.

appreciate any help on this.
2001 C4 (out of warranty)

 

I would bet a bad wheel bearing. A shop could tell you pretty quickly.

 

You can check the wheel bearings by touching the lug nuts after a drive. If the are very hot to the touch you have a bearing going bad. They should just be warm. You can also jack the car up and then grab the tire. You should have very little play.