[Asterisk-Users] Weird Echo Problem

[bails]

Just wondering if someone can explain this scenario:

phone--iaxy--interweb--(asterisk)--IAX2trunk--(asterisk)--SNOM360(SIP)

calls work like a charm.
The iaxy user (in canada) hears very clear audio, no hiss drops or echos.

The snom user (me in uk) has fine audio from the iaxy but always hears 
an echo of himself.  This is only heard on this call, all other calls 
are fine.

So where is the echo coming from??

Thanks

Bails