I"ve got an old S10 that the blower quit two or three years ago and it was the ground had rotted off where it was bolted to the frame. Southern truck, spent one friggin' winter in Detroit 20 years ago and it finally caught up with it.

 

Please describe what you mean by intermittent? If your truck is in auto ac mode, it will start and then kick up to full max with recirc on and this will be louder. If the system feels, in auto, that the kick up is not necessary then you only hear less, turns off recirc. If that makes sense? I will leave my sons home in the heat of the afternoon, about a minute or so later, it will kick up to full auto. This is normal because the system determines this need from all of the sensors.

By intermittent are you saying it blows sometime and then none at all?