Would be very unusual for 2 new V6's to display the same problem. Are you using the same power lead as on the older box ? Have you tried plugging it into a different electrical socket in case there is a dodgy electrical connection in that one? Do you have any noise on you electrical circuit?
-------------------- Services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.