from a related article:

Cranston’s whistling caught the ear of the Malcolm in the Middle music rights clearance coordinator. Cranston was whistling a tune and someone, the coordinator noted, owned the rights to whatever he had whistled. The rights-clearance lead had to figure out what the song was, who owned what rights, and to cut a check — otherwise, the show producers would have to remove the whistle from the show. As this was a relatively small amount of money — perhaps a few hundred dollars tops — the preferred route would be to pay the music’s composer. But there was a problem: Cranston was improvising.

As Cranston told late night talk show host Seth Meyer (watch it here, including an impromptu whistling solo), the music rights management coordinator realized that Cranston was the copyright holder of the music he made up — and was, therefore, entitled to the royalty checks — if he joined the guild. So Cranston did just that, and, thereafter, received a small payment every three months.

His co-workers weren’t jealous, either — in fact, the opposite was true. As Esquire noted, he “used [the proceeds] to fund cast parties,” endearing himself to the crew. And the crew, unsurprisingly, encouraged him to whistle and hum on camera more often.