Joint pain (particularly hips, but can be other joints too) often happens when people start HT, but then tends to go away.
Swimming is good for muscles and somewhat protective of over-stressing them, but like cycling, it does nothing for bone strength, and both these are important on HT. I guess swimming might be useful for joints. Walking (at a level fast enough to be slightly out of breath - can still talk, but not sing) or jogging are good for both muscles and bone health.