"Is it OK to use the AM radio after noon?"

“Is it OK to use the AM radio after noon?” is a jocular one-liner that has been cited in print since at least 1995. The pun is on the two definitions for “AM”— “ante meridiem” (time) and “amplitude modulation” (radio).

Wikipedia: 12-hour clock
The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods: a.m. (from the Latin ante meridiem, meaning “before midday”) and p.m. (post meridiem, “after midday”).

Wikipedia: AM broadcasting
AM broadcasting is the process of radio broadcasting using amplitude modulation (AM). AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is authorized in the medium wave band worldwide, and also in parts of the long wave and short wave bands. Radio broadcasting was made possible by the invention of the amplifying vacuum tube, the Audion (triode), by Lee de Forest in 1906, which led to the development of inexpensive vacuum tube AM radio receivers and transmitters during World War I. Commercial AM broadcasting developed from amateur broadcasts around 1920, and was the only commercially important form of radio broadcasting until FM broadcasting began after World War II.

Google Groups: comp.os.ms-windows.misc
Resources below 80%
Steven Hoke
4/30/95
(...)
* Is it OK to listen to my AM radio after noon?

Google Groups: rec.aviation.ifr
Filing Radar Vectors?
Scot Cline
5/23/95
(...)
... Is it ok to use my AM radio after NOON?

Google Books
Did You Ever Wonder…
By Brendan Lynch
Morrisville, NC: Lulu Enterprises, Inc.
2005
Pg. ?:
Is it ok to listen to the AM radio after noon?

Google Books
I Fail to Miss Your Point:
A Personal Collection of Quips, Quotes, Inspirational Stories and Other Stuff
By Jim O’Bryon
Longwood, FL: Xulon Press
2007
Pg. 407:
Is it OK to use the AM radio after noon?

Google News Archive
7 January 2009, The Munday Courier (Munday, TX), “White’s” by Cynthia White, pg. 4, col. 3:
Is it OK to use the AM radio after noon?

Twitter
Kimi sue
‏@Sister_Bee
Can I listen to AM radio after noon?
#DeepThoughtsWithVictoriaRafieli
6:28 PM - 23 Sep 2014