Sony Receiver STR-D550Z

Question

I have a Sony Receiver (STR-D550Z) that started producing static on the right channels a couple of years ago. We replaced it right away but I've held onto it thinking some day I would look into fixing it or seeing about having it repaired.The static is heared on all inputs and both the A and B sets of speakers. Not sure what other troubleshooting should be done. I know it would be very expensive to have repaired or even looked at but would it be worth my while to purchase the service manual?