FabFilter

You could use the Envelope Follower to simply modulate the source you want to modulate, and set up an XLFO set to random to modulate the modulation level of the envelope follower going to its source.

Thanks for your answer.
Do you mean like this? imgur.com/a/Z8geqev

Not exactly what I want to achieve; I want each snare hit to have a different delay time.
With this setup, it kind of works, but still the delay jumps around inside one feedback cycle, before the next snare hit. Hope my description makes sense.

Try moving the xlfo's Glide knob to zero. Currently you are getting random values but the xlfo is gliding smoothly between them. Setting Glide to zero will allow the random value to stay unchanged within a single repitition of the xlfo.

Thanks.
But still it´s not what I want.
Setting the glide to zero helps somewhat, but the single repitition time of the xlfo is not synced with my signal. It works when I am on the grid; but my track is not on the grid and has random timing, so every new transient should get it´s random delay length, that stays unchanged until the next transient.
another way of thinking: I want to be able to trigger a random value on the xlfo that has unlimited time and keeps that value.