Crackling sound in earpiece

My Binatone Speakeasy 5 corded telephone is making crackling sounds in the earpiece. It is connected via a filter and each of the other 3 phones elsewhere in the house has its own filter. I swapped over the crackling phone for another phone from elsewhere in the house and the crackling moved with the original "noisy" phone. So other phones placed where the noisy one was do not crackle. Could anyone give me some idea what's causing the fault? I am experienced with a soldering iron and I work carefully so I'll not electrocute myself. What components are most likely to have failed/gone noisy?

Normally the line cord. Did you swap the phone including cord or did you unplug the cord from the phone ?

Crackling in the earpiece. Reminds me of my ham radio days.

Normally the line cord. Did you swap the phone including cord or did you unplug the cord from the phone ?

I haven't changed anything yet but after about ten seconds of crackling it gets a lot quieter for a while and about thirty more seconds the noise comes back. I'll buzz the line cord out and see what I can find. Thanks chumpy. Tuesday. I buzzed out both the handset to cradle set cable and the line cord and wiggled them about to see if any connection path would go intermittent. But neither of them did. Any further ideas please? Wednesday. I took the top off the phone and found the cradle switch. I put some switch cleaner in it and the noise abated a little. There's a clue here somewhere!

Hmm I'd say to save the hassle, just get another phone, they start about £5 at Argos

I don't mind the hassle, walkertelecoms. I've now found that having fiddled with the cradle switch the crackling is a bit less. It hasn't stopped completely but it's less. Can I get a replacement cradle switch?

It's all in your signature:suspect:

what does that mean davyboy? That I have to pay. Neither Binatone nor anyone else seems to have spares for my model online so far as I can see.

---------- Post added 30-08-2017 at 19:37 ----------

Another idea I saw on the net is that the software controlling this phone has become corrupted by a nearby lightning strike.