echo-ing sound

I've been trialing a pair of Destiny 1200s for about 3 weeks. My only complaint I have is that the left aid seems to channel on and off, kind of as if one speaker on an audio system was getting turned down but the other speaker kept on playing at the normal volume. It results in an echo-y sound.

My audi can't figure out why this is happening. I'd like to know if anyone has experienced somthing similar?

Thanks.