OP - it could be the tank, it could be gear, it could be any number of things. However!
All these should be ignored for the distractions they truly are.
People may even try to throw in internet connections, hardware playing up, cat walking across keyboard (this last one is actually something I did read when healing a group).
All these should be dispensed with, cast aside, they are falsehoods.

There is only one fault:

Blame the Healer!

If for some reason you do not see this in your group, you should leave anyway as they are obviously not experienced in mmo's and have a lot to learn.