No i havent checked any wiring yet besides the RCA & speaker cables on the amp. It might be the wiring on the speaker because the tweeter doesn't lose volume when the mid-woofer does. If it is to do with the amp or H/U then all the speakers on the left hand side will die together. Knocking on the grill brings the midrange speaker back to life .

I better hope it's not the speaker cone nor the x-over circuit.