Interference (crackly voice in and out)

I am English and I live in Brittany but after reading this forum and attempting to read the french forums, it seems that the problems are the same in France as in the UK.
I use Free.fr which is an isp which provides a package of line rental, internet subscription and european (including UK and Australia!!) and local calls for one monthly fee of 29.99 euros which is a great deal.
I get a connection of 8mb and although this is debatable the download speed is very acceptable. The one big problem is the quality of the telephone calls, both incoming and outgoing. The voices are crackly and difficult to hear so much so that I often have to resort to the mobile to complete a call, which is very expensive.
I previously used France Telecom (same as BT) with no telephone problems but more expensive and I realise that with Free the phone calls are routed via the internet.
I am not at all technical and attenuation and decibels leave me cold but I would be very grateful if you could help me with a few suggestions so that I could try and solve this telephone problem.

What phone as you using to make the VoIP calls ? It may be the codex set on the phone. Make sure its set to G.711 * and make sure you are not running any thing in the back ground, downloads etc.

Are the calls bad to all locations, or is for example local french calls OK?

Hi
The "crackling" is there all the time whether uk or french calls, it is making calls very difficult. The "crackling" is attached to speech, as it normally isn't there. It makes speech break up and almost inaudible. The stronger the voice, the more pronounced the crackling! It is as though the line is failing to pass the speech through and is breaking down. Very difficult to describe.
I have just bought a new phone which is "compatible with ADSL" but the result is the same. I am following the instructions supplied with the "freebox" which is connected to the first "in" telephone socket through a filter. The phone is then connected to the "freebox" via another filter.
Both making calls and incoming calls are no problem, although it does drop calls sometimes.
If i lift the phone and turn it on i get the dialling tone and a funny beep,beep (pause) beep, beep. This disappears when I make a call.
If it will help, I can phone you or vice versa so that you can hear it.
Thanks for your help.

Can you PM me your number and I will give you call during the day see if I can help you solve this.

Hi

You mentioned codecs, will this information help my situation?

Configuration de votre Freebox

Mod�le de la Freebox: Freebox v4 PPP-C
Adresse MAC de la Freebox: 00:07:CB:1F:35:6A

Fonction routeur: Configurer
Fonction Wifi: Configurer
Autres fonctions: Configurer

Nope not really Im still looking into it for you