knocking noise ?? after gear change and letting off.

Discovered a knocking noise when i change gear,Well after when i do a quick change and put in boot down a quiet knock sounds.
Sound like could be engine mount or boot.
its in warrenty but ends this month so could do with sorting b4 its 2 late.
 
Let me know what it is when you find out, mine does it over bumps changing gear/ letting off, just had a driveshaft bearing and steering arms done and it wasnt that.