Noisy/grainy pictures on my digital camera

I have had a Panasonic FZ20 for about 3 years now and in the last 6 mths or so have found a lot of the pics are grainy/noisy. They appear even worse on the pc. My ISO is normally at 200 - 400 during day and 80 at night. Image stabilizer is on unless I take night shots in which case I use a small tripod. I have tried all settings to try and get cleaner, sharper shots but it seems to be worse when there is a lot of contrasting colours or at night. (Night shots are in M mode with MFocus on). Occasionally I do get a crisp photo but generally speaking, they're quite poor. What I do find interesting is that others have posted very similar problems with the same model camera and only recently started having these issues even though initially they got good results. Is it possible that this is a common problem with this model?