Macbook Pro Cd Drive trouble

I have an MBP from late 2007 and recently the cd drive has been acting up. It always made a odd noise when loading or ejecting a disc (or at least i thought t was odd, seems my friend's MBP makes the same noise) but now it won't read discs at all. it just ejects a disc every time. Sometimes I can get a disc to read but that generally takes 2-3 hours of constantly pushing the disc in after its been ejected. I'm out of warranty now though. Anyone else have this problem? Anyone know the cause? Can it be fixed? Is it difficult? Expensive?

Thanks in advance

I guess the 1st thing. Would do was clean the drive. They do get rather dirty over the years.