Is the pressure drop observable only at one faucet or at multiple places?
Try to gently shake the top of the pressure tank (push the top side to create a back and forth movement). Do you hear water moving? Bubbles or waves?
Do you have a water treatment system?
Is the pressure drop downstream or upstream the water treatment system? (Put your treatment system in bypass mode, if the problem continues, the pressure drop is located downstream the system)
