Hey guys, I think something might be going wrong with my Model 5000 amp...I just started experiencing a slight buzz in my left channel which I never had before. It is only noticeable when placing an ear close to the left speaker but it is there nevertheless. Also, over the past month or so I've noticed I'm having to turn the volume control on my Yamaha CX-A5000 pre-amp higher than I did in the past to have decent output. Are there any steps I can take to try & diagnose or will my amp have to be returned?

Thanks very much guys for all your help!!!
Carmine.