Wondering if anyone else that has a SB300 or 301 receiver has a very noticeable hum that can be heard in the speaker when the volume control is all the way down. The level of the hum is not affected by the volume control at all, and it isn't heard when the unit is in the standby mode. I'm wondering if its due to the fact the audio tube is right next to the power transformer. Mark WB8JKR