A trumpet riddle is:
   
Q: What’s the loudest pet?
A: A trumpet.
 
The joke was printed in the book Over 1500 Fantastic Jokes (2002) by Guy Campbell and Mark Devins.
     
   
Google Books   
Over 1500 Fantastic Jokes
By Guy Campbell and Mark Devins
London, UK: Egmonth Books Limited
2002
Pg. 9:
What’s the loudest pet you can have?
A trumpet!
 
6 September 2005, Sudbury (ON) Star, “Smile of the Day,” pg. A1:
What is the loudest pet?
The trum-pet!
—anonymous
   
Google Books
Artful Antics:
A Book of Art, Music, and Theater Jokes
By Jill L. Donahue
Minneapolis, MN: Picture Window Books
2007
Pg. 15:
What is the loudest pet?
A trumpet.
 
Newspapers.com
4 May 2008, The Pantagraph (Bloomington, IL), “Riddle Me This,” pg. ? (last page):
Q: What is the loudest pet?
A: The trum-pet!
   
Twitter 
Anita Searle
@AnitaSearle
JFTD What is the loudest pet?....A Trum-Pet!!
8:09 AM · Jun 10, 2009·Twitter Web Client
 
Reddit—Dadjokes
Posted by u/straightweird February 18, 2018
What’s the loudest pet?
A trumpet
     
Reddit—Dadjokes
Posted by u/superflyracer January 13, 2019
You know what the loudest pet you can get is?
A trumpet.
   
Reddit—Dadjokes
Posted by u/Bakedschwarzenbach June 15, 2019
What is the loudest pet you can get?
A trumpet!
 
Reddit—Trumpet
Posted by u/lilygraceo August 4, 2019
What’s the loudest pet?
...
....
.....
T R U M p e t
 
Reddit—Dadjokes
Posted by u/speechifying September 26, 2021
What’s the loudest pet you can buy?
A trum-pet
 
Reddit—Dadjokes
Posted by u/techtornado March 18, 2022
What is the loudest pet on earth?
A trumpet