Not sure I've had the echo, but anytime I got a new HA I'd have the "speaking thru a barrel"/hallow sound. Generally it would be gone by the time I went back 2 weeks later.
So mine right now are tinny and echo... mine can't be fix because I am capped on my ha sound level and need better ones. but my work is a big house and my clients scream and shout and all the words echo and mash together, some times I get feedback.