Knock sound from the Rear Side - Differential Side

[roumieh2000]

Dear All

I am running a GM Hummer H3 Standard; doing 50Ks on it and I am having an issue back since 3-4 months where I am hearing a knock sound from the back side (probably at the end of the shaft in the cross connection with the Differential) when I press on the gas pedal almost everytime I start moving or even when I am on the go as I am stepping a normally on the gas.

Any Ideas about the type of service that I will be involved in !?!