How can you get between the drum it sound if

In short, you can't.

Not unless you remove the entire drum assembly from the machine and separate the inner and outer drums. Doing this will require that the drum bearing is replaced: it's not an easy job and in any case removing the inner drum usually breaks the polypropylene outer drum. As an ultra budget model, your washing machine was never designed to have the drums separated.

The noise you have is almost certainly something which has fallen from a pocket and then slipped past the front seal into the gap between the drums. You can either wait and hope for the object to break up until the parts are small enough to appear in the trap at the lower front of the machine (check the trap regularly for partial blockages until the noise has been gone for a while), or you can tip the machine forward and shake it to ensure the loose item is at the front of the drum and then try to carefully prise apart the seal just enough to remove the debris. Doing this will damage the seal though and at worst it will need immediate replacement and may stretch it sufficiently that other loose items fall into the gap and can lead to clothing damage as garments slip partially into the gap during a wash cycle and get "chewed".

In practice, if you find a good local washing machine repairer then they'll have their own favourite tricks to recover loose debris. I've personally cut access panels into the outer drum and then made good afterwards but not all washing machine repairers can apply boat hull repair experience to the task!

Note that almost all Indesit W123's will now be well past their five year design lifespan. If your machine has any other issues then now might be a good time to take advantage of the current low prices offered by retailers and to also avoid paying the additional VAT which will be added when it returns to the old 17.5% rate in January.

Sorry not to be able to provide a quick and easy fix, but you can prevent the problem in the first place by always checking all pockets and hems for coins, cards, keys etc. before washing and to ensure that socks, tights, and similar items are washed in a closed net bag. I hope that my reply has been of some assistance in at least preventing you from making the fault any worse and only ask in return that you rate my answer.