The problem with injecting resin between the core and skin of a delaminated area is that it doesn't fix the underlying reason for the delam in the first place (usually caused by a bad bond to the core, often because the core face was contaminated before laminating).

Alternatively, and usually a more permanent/sturdy fix for delamination, depending on the side of the delamination, is to grind the affected area away (including one skin and all the foam), leaving just one intact skin remaining.

Vac bag a new core into place, fair the core with a torture board to the surrounding skin, apply new second skin with suitable overlap on the surrounding skin, fair again with torture board and paint.

It does depend on how big an area the delam is though. If it is smaller than the size of your hand, injecting resin may easier, but it may not fix an underlying problem with the core to skin bond.

Having said all that, a crunching sound may indicate that the core has been smashed during a collision...in which case the original core to skin bond in that area is fine, but injecting resin may still not repair the damage well because you can't see the extent of the damage.

If you've got the facilities and skillz, replace the core, it is the solution with the least chance of failing.