Constant high cpu usage of "system_server - BluetoothPhoneService"

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

Has anybody else encountered this issue?

Any advice would be most appreciated. I would be pleased to install any other software which may help provide more info.

I posted this in the Nexus 5 forum with no replies, but then realized it is probably better suited here.

Thanks,
Mike.