Have a prominent knot on my left achilles. Running shoe switch ( from NB to Soconys- they fit like a glove but about crippled me) plus hill work was the culprit. Early 90's. In my case swelling comes and goes. At some points ceasing running for two weeks or more, and then easing into running again, taping the ankle to limit the lower heel to toe angle and flex, and heel lifts in the shoes all help to lessen the stretch on the tendons. In a bucket of icey water as soon as the shoes and socks are off. This has occurred to the right also but not to the same degree. ( And at this stage of the game I do no speed work and hill work is just on the treadmill.) Started one ski season with a very swollen tendon in Surefoot boots. The old hard foam. Heel firmly locked in. Fit like a second skin, but the tendon hurt like hell for awhile. The late George Sheehan( the Running Doctor), said something along the lines of you try all kinds of remedies to alleviate the condition in vain, and it will get tired of tormenting you and go away on it's own. Re-occurances seem to come with no reason. And you are correct- getting old sucks, but it sure beats the alternative.