Apple on Thursday issued a firmware update for its entry-level MacBook notebooks to adjust "fan behavior." And it wasn't talking about Apple users.

The firmware update, which can be downloaded from the Cupertino, Calif. company's support site, is in response to ongoing customer complaints about overheated and/or noisy MacBooks, the newest model in the Intel-based portable line.

This isn't the first MacBook heat issue acknowledged by Apple. In June, it alerted users that some machines may have left the factory with a piece of plastic blocking the rear air circulation vent. And in a related release, Apple issued a May firmware patch for the upper-end MacBook Pro that also addressed heat problems.

According to users commenting on Apple's own discussion groups, the MacBook firmware update makes a notebook's fans run continuously, albeit at a low speed. When necessary, the fans will speed up to move more air through the case.

Some didn't care for the change.

"The sound it produces now is only a bit more bearable than the mooing sound I heard from time to time," wrote someone identified as "phjo." "The only good news is that I don't remark the whining sound anymore (although it is probably still present)."

Others, however, reported that they could not hear the fans, or if heard, that the sound was barely audible. Among them was at least one wit.

"Next to random shutdowns the two biggest complaints from Macbook users are excessive heat and mooing," wrote "Agent McKay."

"Now we have an update that appears to fix both issues, yet folks are now complaining that in a room with no air conditioner, no music playing, no tv, no voices, you can hear the fan running if you put your ear next to your Macbook. This is unacceptable! I think Apple should also include a pot of gold with the update to compensate for the horrible fan noise. I'm calling Steve right now and demand my pot o' gold!"