Loud crackling sound during voice calls only (iPhone 4)

Here's my problem...

when placing calls, i get :-Loud crackling / static soundsfrom the ear piece &from speaker (if speaker-phone is selected when placing a call)Also, from the earphones when connectedMusic / videos seem to work fine (intermitten)sometimes it crackles - sometimes its fine

What I've done:-

cleaned out the earphone connector & dock connector with a cotton budused a hairdryer on the earphone connector & dock connector with a cotton bud (helped a little)rebooted the phone (no joy)restored the phone to factory settings (no joy)removed any apps that was installed prior to the crackling sound (no joy)

Other than the iPhone not being able to function as a phone - everything else works fine.

Please help...

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