Oh that's wierd. Does your receiver have mechanical input switches or something like that ? Maybe turn down the volume and switch back and forth between 5.1 inputs and something else a few times...

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8