Thanks for the answer !
So you mean the way the Shrike is currently implemented in the mod, with a lock-on tone, is not realistic ? Interesting.
Searching the web I found this and this which seam to describe the launch sequence of the Shrike. Unfortunately, the first image is out of focus and the text is unreadable. On the second image, top right, there is a sentence regarding "audio tone", which may indicate the pilot could hear when the seeker was detecting a signal, prior to launch. But the text is incomplete, so I'm not sure.
I also noted here that it is said the guidance system was limited to certain radar sources. That makes sense of course.