Chris

Try it without the amp first, to see if it gets any worse. You're pointing at Winter Hill, which is enormous and very powerful, and you're not even that far away from it. I am surprised you need an amplifier at all. My mum receives from Winter Hill, unamplified and without issues, and is significantly further from the transmitter than you.

If it gets no worse and no better with the amp removed, then the amp isn't the problem.

An amp located next to your TV set isn't likely to make a vast difference and if you have problems on your cable, the booster will simply amplify all the noise on the cable as well as the signal. If you do need amplification, then ideally it should be mounted on the masthead with a power unit located in your living room by the telly. You'll need someone in to set that up for you unless you're competent and comfortable working at heights.

You are more likely to be suffering from degraded cable or connectors, or a misaligned aerial.