I recently purchsed the Onkyo tx-sr605 and the tx-sr505 from an online vendor. I hooked both receivers up to the same speakers to test each unit when they arrived and for some reason the volume on the 505 is much louder than the volume on the 605. For example when both are set at volume level of 50 the 505 sounds much louder than the 605. Could this mean that the 605 is defective or damaged?