Interference using AV / digi sender

[CW1]

Hi,
Bought an AV sender like this one for partner. There's sound and eventually got pic but also a thick line that scrolls on the receiver tv, with an awful thump-like noise. The tvs are on the same outside wall, in adajent rooms, with only the hall and 2 doors separating them.
I tried the AV sender in my house, receiver tv upstairs, and I got the same prob so I've taken that back to the shop.
I use a scart type digi sender (similar to this) with no prob but when I try that one at my partner's house, he gets the same prob with interference. Have tried all 4 channels. The only thing I thought might interfere with the signal is a broadband/phone filter in the hall but taking that out makes no difference.
Any ideas or other options ? Or will I have to buy him SKY multi room !!?? Arrggghhhh !

[scaniavabis]

Is your broadband coming from a wireless router? I had exactly the same problem. The interference will be the wifi network if so. You'll struggle if this is the case, I had to turn my wirelss off to use my sender and eventually threw it away as changing channels on the sender didn't work either. I even but my Orange Livebox in a jiffy bag lined with cooking foil, that worked to a degree but you can imagine what it did to the wireless network.

[CW1]

Thanks for your answer but no, broadband router's not wireless. I just can't think what could be causing the prob :(