Default JVC car audio bluetooth dropouts

I have a JVC KD-R821BT bluetooth car stereo paired to my S4. Everything is paired up fine, but when playing audio from the phone through the JVC unit there are frequent drop outs - i.e. a 3-second silence every minute or so. It happens with any app (e.g. Google Play Music, BeyondPod).

I don't have this problem when using the phone with a Parrot Mki9100 in our other car, so presumably the issue is related to the JVC unit.

Has anyone else had this sort of problem??