Older metal c.b.'s show cracks, often from the wood framing expanding/contracting with the seasons or HVAC changes because they are fastened through to that framing rather than just drywall, as are paper-faced metal beads, clinched-on and "speed bead"; http://literature.usg.com/pdf/J1445.pdf
Clothes taking longer to dry?
Clean the dryer screen in HOT water if using fabric softener sheets.
They leave a residue that impedes air-flow, costing you money.
Clean the ducting in the last six months? 17,000 dryer fires annually!