A couple of Google Books search results yield matches from as early as 1953. From Television Magazine, volume 10 (1953) [snippet view]:
No more a-c power line "glitches" (horizontal-bar interference)— because camera filaments are operated from a separate d-c source.
A check of the Internet confirms that Television Magazine began in 1944, which would make 1953 the expected year for volume 10 to appear. Also unconfirmed, but probably from 1953 or 1954 is this instance from Journal of the Audio Engineering Society, volumes 1-2 (1953–1954[?]):
The character of the noise voltage was found to be rather important, and tests showed that a smooth type of hiss gave best results. Generators having high-level spikes or "glitches," even when followed by some degree of limiting in succeeding amplifiers, did not produce as good an effect as those having smooth, random electrical noise output.
The earliest indisputable instance of the term in Google Books search results, however, appears to be from an advertisement for Bell Telephone Systems that ran in (among other periodicals) the October 15, 1955, issue of The Billboard:
They Talk of Pigeons and Glitch
"Pigeons" are not birds to a Bell System technician. They are impulse noises causing spots which seem to fly across the TV picture. And when he talks of "glitch" with a fellow technician, he means a low frequency interference which appears as a narrow horizontal bar moving vertically through the picture.
Robrt Chapman & Barbara Kipfer, Dictionary of American Slang, third edition (1995) trace the term only as far back as 1962, but this reference work identifies the source as being "fr[om] German glitschen (or Yiddish glitshen), "slip."