My driver's side boot has been split for nearly a year and narry a sound can be heard from the joints. When I lived in Alaska it was VERY common for boots to split and we just waited until the joints nearly gave up before replacing and that's pretty much the approach I've been taking on all my...
It sounds similar to what I was having happen and at one point I started to see hints of pink/red in it, which pointed me to the water pump. My water pump was leaking and had to be replaced.