What does it mean that "We weren't exactly hitting the sweetest notes"?

What does it mean that "We weren't exactly hitting the sweetest notes"?

The script in the movie "The Bucket List: goes like:

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Carter Chambers: Dear Edward, I've gone back and forth the last few days... ...trying to decide whether or not I should even write this.
 In the end, I realized I would regret it if I didn't... Unknown...so here goes.
Carter Chambers: I know the last time we saw each other... ...we weren't exactly hitting the sweetest notes. It certainly wasn't the way I wanted the trip to end.
I suppose I'm responsible, and for that I'm sorry.
 But, in all honesty, if I had the chance, I'd do it again. Virginia said I left a stranger and came back a husband. I owe that to you.
 There's no way I can repay you for all you've done for me...
...so rather than try, I'm Just going to ask you to do something else for me. Find the Joy in your life. You once said you're not everyone. UnknownWell, that's true.
You're certainly not everyone. But everyone is everyone.
My pastor always says: " Our lives are streams...
 Carter Chambers...flowing into the same river... ...towards whatever heaven lies in the mist beyond the falls. "