What's wrong with my internet?

My internet is rather annoying to say the least...

Sometimes it will connect and stay connected for a week straight. Then other times it will be constantly disconnected unless I unplug it, plug it back in, wait for it to connect, and it will stay up for about a minute or so, before disconnecting. The phone also gives a slight cracking noise recently so I'm wondering if it's the house's wiring, but the phone line works and is tolerable.

We have a wired phone so there's no interference from that, and BT gave a 100% phone line connection recently, so it's not their fault.

Rather than calling my ISP straight away I'd like to know if anyone could help me here, since I don't want to wait for 3 hours on the phone for them to tell me to unplug the unit and plug it back in.

Thanks a lot, Sam.