HCA: Hermit Crab Association

I just got another large crab from a friend who no longer wanted her setup. The crab is the largest i now own and he was in a 20 gallon with no hiding places and almost nothing to climb. I took shells from my 90gal that would fit him and then put them in the 20gal he came in and he changed into the new shells. I then took his old shell and put it into my 90gal. The reason for this is because i have a large crab who is the boss in my tank and he is very picky about shells and had been wearing the same one for months and i new he would really cause problems if that crab came into into his territory with a big beautiful shell on that my crab had not yet tried on. My crab in the 90gal changed into the new crabs shell and the next morning i put the new crab in the 90gal. Of course my guy comes running up and the new crab starts chirping. My crab has the new crabs shell in his graso and the new guy is pulled back in his shell chirping.
Why do they chirp? I never here my crabs chirp. But do they chirp when they are scared or what?
Also there were some fake plants in the new crabs original 20gal that he came in and they are shredded. Is this because he did not have anough room and stimulation? Or is it just because the crab likes to tear fake plants? I have many fake plants in my 90gal and my crabs have NEVER bothered them. They climb them all the time but never shred them.

Chirping is usually a sign that they are unhappy or upset with something.
Did you give everyone a quick dip in the fresh water so that they all smell the same and nobody seems like the 'newbie'?

I've had exceptionally large crabs turn absolutely destructive in small spaces. The one jumbo I had to keep in a smaller tank destroyed three plastic plants before I had their new enclosure done, and then never did it again. Carol of Crabworks used to note that Jon and Kate would wreck their tank overnight on days when she couldn't let them out to wander, too. It should get better with time now that he has space to move!