Noisy Receiver

I recently purchased a 5.1-channel AV receiver to complete our 2-person theater in the River House. Paired with some high-quality speakers that I used with my last surround sound system I am quite pleased with the fidelity and sound stage. Jeanine and I rented Oppenheimer which proved to be a perfect choice for testing the system and an incredible movie. Eventually, however, l noticed distinctly audible white noise during times when the soundtrack got very quiet. I grabbed my signal generator and oscilloscope to verify the issue. The oscillograph above shows a fairly significant noise component superimposed on what should be a pure sine wave. It should be noted that this is most perceptible only when the volume is turned up quite high. Even so, I must now decide if I will return the receiver because of this issue. It would be a no-brainer if the system did not sound so good otherwise. I have just under thirty days to decide.