Is the problem in all of your drivers, or just
in one box?
If it is just
in one box, swap them over and see if the problem remains in that box or is now in the one with which you swapped it. If this is the case, it is not the
speaker.
In testing – I would first remove all the effects and processing gear from the signal path. If it were me, I would actually
plug a signal generator directly into the amp and
power it up at a low frequency (longer wave form and therefore longer travel on the
cone).
If you do not have a signal generator, you can download programs that will do this for you and run off of a computer or just use a CD player. I have a box with a 2 gang 10K pot that I use to test older amps that do not have volume controls on them. Essentially, you want to limit the number of potential problems in the signal path. Every
connector, cable and piece of equipment is a potential cause for fault.
Once you have run the speakers off of the amp and there is no crackle or other obvious problems, I would then run the signal through the
desk and then use a mic and then add in the other equipment piece by piece. Also swap over cables if any test fails and explore the cable issue before proceeding to the next step.
If you do push on the
speaker, make sure that you apply even pressure or you will cause the
speaker to rub due to the angle at which you are pushing it, rather than have it rub due to damage that is already there. The rub is generated by either the spider failing (the corrugated disc that sits at the bottom of the
cone and holds the
cone in a central position), there is damage to the
voice coil or the lacquer that coats the
voice coil has blistered (due to excessive heat) or some crap has fallen between the
voice coil and the former. If this is the case, the
speaker can be repaired and it may be worth having them inspected by a repair company. Try to find one that only deals with speakers as opposed to a general tech outfit that can also repair them.