Happened to me as well and I also thought the same but it turned out to be a seat noise instead.
Park your car at a quiet place. Roll up the windows and turn off the engine.
Now just jump a little bit and do some moves on the seat. Most probably you'll hear that noise.
In my case it was a very minute noise and it vanished it self after sometime. At least it is now down to such level which is unnoticeable.