I had a lot of this kind of maintenance to do when I moved into the new place!
Wires exposed to the atmosphere will start to corrode. Water can tend to make it worse temporarily. I simply found all the dodgy phone wire connections, sanded them back to copper, twisted em tight and taped them up to exclude any more moisture. No more, snap crackles or pops!
A similar problem can of course occur in the street/exchange wiring but they are usually a little more pedantic in doing a good job the first time. It costs to make a unpaid maintenance call. Home owners tend to take shortcuts so the problem is more likely in something they have done!
Also had similar problems with CATV. Lack of good earthing connections at plugs was more an issue than actual signal level. (ie the signal to noise ratio was bad even though there was adequate signal strength)
Sorry for the waffle on...
Cheers Bob (Aussie >>out, can anyone tell me if there is something else I can try. And,