2007 Prius Bluetooth suddenly stuttering

I've had no problems using the Bluetooth to talk on the phone through the stereo speakers for the 7 years I've had the car -- through various phones (currently iPhone 6s). This week I had to replace the auxiliary battery, and all of a sudden, the Bluetooth/phone doesn't work: sound is a pulsating stutter. Not sure if timing is a coincidence? (Also upgraded to latest IOS). I have deleted and re-paired the phone. Not sure what else to try. Has anyone else experienced/fixed?