Callers hear their voice echo if I take/make calls using Apple Watch

I'm having a bit of an annoying issue with using my Apple Watch for telephone calls and wondered if anyone has experienced the same issue?

When I either receive or make a call from my Apple Watch (which is a Series 2 running the latest software). The person I am talking to, tells me that they can hear an echo of what they have just said, and this then makes it difficult for them to hear what I am saying.

I have also spoke to someone via a landline, and they tell me that the echo is there too.

The weird thing is. While I am on a telephone call and the person on the other end mentions about the echo, if I then hand the call off on to my iPhone (iPhone 7 Plus with iOS 10.3 installed) the person tells me the echo has gone.

I was wondering if anyone has been able to get to the bottom of this issue?

I cannot really say how long this issue has been going on, apart from it wasn't there when I got the Apple Watch back in December.