Sadly after struggling for too long, I finally "tore" something when lifting a heavy box - fast forward 3 months and I have a lot of damage to my left hip, which has probably been going on for years, but I tried to ignore it, 'cos that's what us mums do!
I have to have a hip arthroscopy, bone shaping, cartilage repair, will be on crutches for weeks, and absolutely no running in the future, ever! Mind you, I can't walk beyond 20 minutes at the moment anyway. 6 months ago I was hiking in the Rockies, white water rafting, now I can't even do up my laces!
Sooo - advice - don't ignore those niggles - get them properly evaluated by a sports doc, who knows their stuff BEFORE it turns into something more serious.
Good luck to all doing c25k - I really enjoyed it, don't regret a minute of it, and will be forever proud that I "did it!"