A music riddle is:

Q: What do you get if you cross a lamp with a violin?
A: You get light music.

The “light music” pun has been cited in print since at least 1999.


13 July 1999, Home News Tribune (New Brunswick, NJ), “It’s a joke!,” pg. C12, col. 5: 
Q: What do you get if you cross a lamp with a violin?
A: You get light music.

Twitter
budmanandbooger‏
@budmanandbooger
Q: What do you get if you cross a lamp
with a violin?
A: Light music.
2:07 PM - 12 May 2009

Google Books
Sensible Nonsense.. Frank’s Comic Pack:
Humour Pack Series
By Frank Paul
BookBaby
2014
Pg. ?:
Q: What do you get if you cross a lamp with a violin?A: You get light music. “

Google Books
Music Jokes:
Funny Jokes about Music!
By Johnny B. Laughing
CreateSpace Independent Publishing Platform
2016
Pg. ?:
Q: What do you get if you cross a lamp with a violin?
A: You get light music.

Twitter
PHP tweetLater‏
@PHPtweetLater
Q: What do you get if you cross a lamp with a violin? A: You get light music.
7:14 AM - 25 Oct 2017

Twitter
Lucky Score‏
@LuckyScoreNet
Q: What do you get if you cross a lamp with a
violin?
A: You get light music.
#Joke from #MusicJokes in #Jokes, #Humor and #Satire
5:41 PM - 13 Jan 2018