I've heard it said that fiberglass antennas are noisier than aluminum. But I have found that just isn't so. The Imax I use receives noise on some days and no noise on other days. So - if it is a noisy antenna by nature; then how come there is no noise with it sometimes. That argument that all fiberglass antennas are noisier just doesn't hold water - sorry to say.
But I will agree with just about everything else you said NB . . .
What you said is absolutely true. Just because the antenna has fiberglass around the radiating conductor does not mean that it is noisy. Any number of variables are in play that can affect this, including but not limited to where the antenna is mounted.
The DB