That's when you send him a bonus because that guy would be a plumbing genius.
Anything mechanical that involves water is going to involve rusting or decay. Flushing and whistling are completely different issues and he could explain it to you if you asked him.
The parts inside a toilet are pretty basic and if you are the slightest bit handy, it wouldn't cost more than $30 plus the time and aggravation to learn how to do it.
In most cases, plumbers are paid to eliminate your aggravation, not perform feats of diagnosis that rival Dr. House.
Every service that involves making house calls is going to have a high cost in relation to the amount of time spent to fix a problem.
Imagine how much you would charge if someone asked you to come to their place to edit an essay.