Same here. I’ve known of it since the 90s. I could never recognize it unless pointed out.
Well duh… anyone can detect Wilhelm’s German accent. 
Groucho Mark claims he started the laugh track. Someone in the studio told off color jokes to generate the laughter.
Sheb Wooley of Rawhide made the Wilhelm Scream.
BTW, if you look at the credit list of the actor who played Pvt. Wilhelm, Ralph Brooks (born Charles Emil Muller from Baltimore), you’ll notice that he’s rarely credited. I’ve seen his name in some TV episodes, and he’s never easy to spot.
They also used laughs from I Love Lucy for decades as a general laugh track. According to Desi Arnaz, Lucy’s mother, DeDe Ball, was at every filming, and her laugh was unmistakable.
Sheb Wooley voiced the Scream for a 1951 movie called Distant Drums as an uncredited voice-over for some poor soul who got eaten by an alligator. (He did play one of the minor characters in the movie but his voice work was uncredited other than in a studio memo listing voice actors. Then the Scream got reused in 1953’s The Charge at Feather River when Pvt Wilhelm gets shot by an arrow.
Here is the raw recording of Sheb doing six screams along with some directorial well, direction.
https://freesound.org/embed/sound/iframe/675810/simple/full_size/
From IMDB:
Pvt. Wilhelm: Yeah; I’ll just fill my pipe!
[gets shot by an arrow in the leg]
Pvt. Wilhelm: AAH!
They say it’s silly. They call it goofy.
But who among you can honestly say that if you got bit by an alligator, or fell off a cliff, the last thing you did wouldn’t be to make a noise a lot like that?
Or having a ton of science material fall on one of the birds at the Kurzgesagh YouTube channel. 
(Just spotted the scream when the material falls on the birds in this scene from 3 months ago, they are also a European production)
For the longest time, I thought it referred to the Goofy yell, and wondered why I could never notice it.
