Help with constant "system_server" high cpu usage

I am running 5.1.1 on my Nexus 5, and have recently noticed reduced battery life. When running Quick System Info PRO, I notice that "system_server - BluetoothPhoneService" is constantly consuming anywhere from 15-60% cpu, usually 20-30%. I have tried everything INCLUDING restoring all the original factory ROM's, starting with 5.0 (LRX21O) up to 5.1.1 (LMY48I), yet the issue persists. Toggling Bluetooth doesn't help any. Bluetooth functions normally when needed, but is usually kept off.

Has anybody else encountered this issue?

Any advice would be most appreciated.

Thanks,
Mike.