Bluetooth Earphone Sound Quality

I recently bought a Vivoactive 4S so that I could listen to music on my runs, without taking my phone with me. I own a pair of Taotronics BH076(?) bluetooth earphones which have served me well over the years, and paired fine with plenty of different devices. 

However, when using them with my Garmin, whether it's using Deezer or the music loaded onto the watch - the sound quality is awful - it's full of crackling and popping, like an old vinyl record. It's as if the earphones are a long way from the watch - or there is some interference. This happens whether I'm in the house or out and about and the earphone's bluetooth receiver is on the same side as the watch. 

I asked Garmin, and they basically told me to buy way more expensive earphones. I would, but I just spent a whole load of money on a smart-watch. Plus, my earphones work fine with every other device I use. 

Anyone got any ideas what's causing the issue, or how I could go about fixing it? (I've updated all the firmware, etc. and the watch itself is more or less on factory settings).