If you have manual awnings as do we, there are a couple of fixes we have done.
If they rattle while retracted and you are driving, there is a "U" shaped clamping device part way up the arms intended to hold the inner and outer arms (upper and lower when extended) secure. I carefully closed the legs of the "U" a tad. Solved our problem. Also, make sure the plastic locking knob lower down the legs is tightened.
To minimize the rattling when the awning is deployed, we, like ThomB, use tiedowns to anchors (or five gallon buckets of water, depending on where we are), but we include a short length of shock cord between the tiedown and the anchor.
Also, on the outboard end of the upper leg is an odd shaped "knuckle" that slides along the lower leg and locks at the outboard end of the lower leg. With or without anchored tiedowns, those things rattle. We cut a 2" x 3" piece of exercise mat and contact cemented it to bottom of the knuckle. Stopped the rattle. It doesn't show to passersby. Yet another use for that mat.
If your awning is electric, none of the above applies.
Fair Winds and Following Seas