Creaky knees - I'm only early 40s

[squidgesquodge]

Various issues mean I haven't had the time or the inclination to do any exercise since Christmas. I wasn't doing much before then but was running 3x a week and doing 5k each time.
In the last week, I've started running again but doing couch to 5k again from around the middle (so 3 or 5 mins running interspersed with walking) and am also doing some squats and lunges and arm weights.
My knees sound really creaky. What can I do? They're not hurting, just sounding like a door which hasn't been used for a while. Will they loosen up in the way a door would or am I going to cause myself an injury?

Is the creak like a proper squeaky type creak you can feel, that doesn’t go away? Just that when I’ve had tendinitis the tendon has ‘creaked’.

In January 2017 I had a dodgy knee and a wobbly ankle. I've always done some yoga, but had somewhat lapsed by then. I started doing my old 20 minutes a morning regime - a few warm ups, cat cow, 4 x sun salutations, triangle, warrior + variations, eagle, tree, extended stork and dancer. I usually put in a few other poses that vary from time to time. After about 6 months I realised my knee no longer hurt and my faith in m new stronger ankle was such I could wear heels again. Since then I've lost 2.5 stone and started other exercise but for joints I think yoga is the way to start.