Actually, steam traps behave in almost exactly that way. Tapping on them can
get them to stop banging,  but it's usually a temporary fix.

This is kind of a different scenario, though. Here the technician does have
the expertise and fixes the problem, though it seems like his hourly rate is
high. I'm talking about the guy who comes out, replaces ten steam traps,
sends a bill for $5,000, and still doesn't get the heating system working.

I'd gladly pay $300 for someone to knock on a steam trap if that got the
system working.